Selling stocks that have served investors well is always a difficult decision to make, but when the negatives pile up, it is wise to let go quickly.

Thus, consumer food product maker General Mills (GIS - Get Report) and Wall Street bank JPMorgan Chase (JPM - Get Report) look fully valued. Investors should ignore the 2% to 3% dividend yields and the reasonable records of rising payouts.

Instead, focus how expensive they are, meaning that it is time to book profits.

After a rock-solid 23% year-to-date gain, General Mills is running out of steam.

This stock has outperformed peers such as Kellogg (up 14% this year), and it is also way beyond analysts' median target, which means it runs a risk of correction. Shares of rival Post Holdings, meanwhile, have upside left.

General Mills has had zero sustained profit growth since 2011, and share buybacks can only conceal the drop in earnings per share. Revenue growth has been equally disappointing.

Meanwhile, the company's brands, such as Betty Crocker, Cascadian Farm, Cheerios, Haagen-Dazs and Pillsbury, are losing their grip in their markets.

Perhaps most damning, debt has been climbing and stands at $8.4 billion.

In terms of valuation, the stock's metric of 25 times is a huge premium to its own five-year historical average of less than 19 times.

Annual earnings growth over the past five years was meager, at 3.82%.

And looking at dividend income shows that payout is too much and unsustainable.

The company's dividends could soon be affected by the apparent lack of upside potential in the stock. Granted, dividends are a sure-shot way to get fixed income payouts every quarter, but General Mills looks riskier by the day.

From a payout ratio of 30% to 40% in the 2000s, the company now pays well over 60% of profits as dividends. This would make sense if profits were growing.

Strangely enough, profits are scheduled to show less than 7% growth annually over the next half decade, compared with more than 14% for the industry.

The writing is on the wall: There is no money in those once formidable war chests. Investors should get out soon.

The other dangerous stock is JPMorgan Chase, which is one of the most revered banks in the industry, but the truth is, its earnings growth is expected to be slower than the industry's for the next five years.

Yet, JPMorgan Chase carries a nearly 80% premium valuation based on its price-earnings-growth ratio of 2.69, compared with the industry average of 1.51 for the next five years.

Why are investors ready to pay more? There is no clear answer to why investors are drawn to the bank's over-hyped reputation.

Analysis firm Berenberg has seen through this facade and cited overvaluation as a reason for its sell rating.

JPMorgan Chase is certainly not the cheapest stock, nor is it the best-performing bank. Bank of America (PEG ratio of 1.72) and Wells Fargo (PEG ratio of 1.44) are more attractive.

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Bernstein analyst John McDonald also doesn't suggest there is enough upside in JPMorgan Chase's shares at their current valuation.

The 2.8% yield and five years of dividend growth may seem pretty sharp, but the stock has run its course based on every technical and fundamental parameter.

Citigroup analysts contend that banks are trading range stocks, and a better time to add fresh longs would be when sentiment is down.

JPMorgan Chase Chief Executive Jamie Dimon has been losing a clutch of talented people, a major negative.

That isn't to say that his leadership has been terrible, however. Among Dimon's major achievements is helping JPMorgan Chase stay afloat in the wake of the London Whale trading fiasco.

As he will find out, the stock will eventually have to justify its premium valuation, an arduous task for the bank. Smart investors should steer clear.

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.