The broad-based S&P 500 may be down four of its first five trading days in 2014, but you can hardly tell the difference with 432 stocks hitting a new 52-week high yesterday compared to a minuscule 41 new lows, according to Finviz. For skeptics like me, that's an opportunity to see whether companies have earned their current valuations.

Keep in mind that some companies deserve their current valuations. Medical device behemoth Medtronic (MDT 0.14%), for instance, has exploded to new highs over the past week despite its only announcement being the relatively small $160 million purchase of privately held implantable device maker TYRX. Medtronic's tight cost controls, heavy emphasis on emerging markets, and stranglehold on spinal implants, coupled with an aging baby boomer population domestically, make the company worth a look for buy-and-hold investors.

Still, other companies might deserve a kick in the pants. Here's a look at three that could be worth selling.

You forgot the growth!
Who in their right mind would have thought that Internet search engine Yahoo! would more than double in its share price in 2013 after doing absolutely nothing for about a decade?

Things have certainly changed around Yahoo! HQ with a new sheriff in town, CEO Marissa Mayer. Mayer has Yahoo! focused on driving its mobile viewership, as well as in promoting its home page as a one-stop shop for news. Just this week at the Consumer Electronics Show, Mayer announced two new online magazines, Yahoo! Tech and Yahoo! Food, introduced a news tracking app, and touted that Yahoo!'s services attracted more than 400 million monthly mobile users last fall, a new company record.

While there's finally excitement brewing at Yahoo!, it's really for all the wrong reasons. What matters most to Yahoo! is its remaining investment in China's e-commerce behemoth Alibaba which will likely IPO in the U.S. later this year. I would contend a vast majority of Yahoo!'s 2013 run-up was based solely on Alibaba and not on its efforts to retool its mobile viewership or improve its front page.

Don't get me wrong -- If you look at Yahoo!'s bottom line you will see improvement. But in fiscal 2013 revenue is expected to be in a range of flat to down 1% while growth in 2014 is forecast around 2%! The problem is that display revenue continues to be weak, while mobile ad revenue offers weaker margins but greater long-term growth potential than PC ads. In other words, Yahoo! is stuck between a rock and hard place right now in its transformation. Once Alibaba goes public, I have a strong suspicion investors are going to catch on to that fact and could punish Yahoo!'s share price.

I believe Mayer is doing the right thing, but I'm certainly not feeling Yahoo!'s share price here above $40.

Held back a grade
I'm usually not one to give investors the dunce cap, but whoever is buying shares of online and on-campus educational provider Apollo Group (APOL) needs to be sent to the corner, face the wall, and seriously think about they're doing.

For the second time in a matter of months Apollo, the parent company behind the University of Phoenix, exploded higher following an impressive earnings-per-share beat. For the first quarter of 2014, Apollo delivered $1.04 in EPS, $0.14 better than Wall Street expectations, according to my Foolish colleague Jeremy Bowman, but still managed to miss revenue by $5 million. What really seemed to invigorate investors was the company's willingness to stick to its previous forecast of $3 billion-$3.1 billion in revenue for fiscal 2014 and net income of $400 million-$450 million.

Although its profits remain robust thanks to very strict cost controls, Apollo has seemingly done nothing more than hit an iceberg and put gum over the holes in its hull. The first quarter also brought a 17.7% decline in overall enrollment and an even worse 22.9% dip in new student enrollment. A combination of tougher lending practices to students, increased regulatory oversight, and less disposable income for younger adults is making Apollo's push to boost enrollment an ongoing lost cause. 

Shareholders in Apollo have to be wondering how many more years Apollo can withstand before the cost reductions can no longer mask this precipitous decline in student enrollment. We know as investors that cost-cutting isn't a long-term strategy for success, so why would you even consider chasing Apollo higher when revenue continues to fall by double-digits?

If a tree falls in the forest...
I admit that there are certain sectors I don't like very much, and the paper and paper products industry is one of them. Despite delivering what is close to a basic necessity, growth is often in the low single-digits, debt levels are usually astronomical, and many are tied at the hip to the global economy -- meaning you have to nab them near a trough; otherwise they can be a poor hold for the long run. That's why today I'd suggest it could be time to make a new year's resolution to run away from Montreal-based Resolute Forest Products (RFP).

Like Yahoo! and Apollo, there have been some notable bright spots that somewhat explain this recent surge in Resolute Forest's share price. For example, the company's pulp business saw a 2% increase in shipments and a $5 per metric ton increase in price, as efficiency improved and total market pulp operational costs fell 4%. In the words of CEO Richard Garneau, "improvements in volume, transaction price, and costs led to the best quarter our pulp segment has seen in two years." 

Beyond a few notable standouts, though, stood many of the same challenges that have existed for years and look poised to stymie any potential for meaningful growth.

For one, operational costs remain high throughout the industry, not just with Resolute Forest. The company is doing what it can to improve efficiency, and we are seeing a fair number of acquisitions in the sector to improve synergies, but these higher costs aren't likely to go away anytime soon.

Secondly, the demand for Resolute's products is wholly hit or miss. There are few regions of the world where magazine or print subscriptions are flying off the rack, meaning demand for coated or specialty papers is still moot at best over the next couple of years and perhaps even longer.

Finally, it's a matter of Resolute's growth potential relative to what investors are risking by owning this stock. With Resolute Forest you get no dividend and are privy to an organic growth rate of perhaps 1% with a net debt position of $333 million. While not overwhelming in terms of debt, the 1% organic growth is a point of concern when the company is valued at a whopping 16 times forward earnings following its latest romp higher.

I believe the answer to the age old question is "if a tree falls in the forest"... short-sellers will hear it!