Despite recent downgrades to its stock, electronics manufacturing services firm Plexus ( PLXS) has continued to defy Wall Street, swimming upward and bobbing at its 52-week high. After Plexus' first-quarter earnings report in January beat consensus expectations, the stock charged up more than $7 in a day to $30.79. That climb has continued, despite analysts' caution about growing competition, a possible slowdown for Plexus' largest customer, Juniper Networks ( JNPR), and superficially high valuation. But investors aren't listening. The stock ran up more than 2% on Monday to $36.63 to set another 52-week high. "The run-up here is a bit excessive," says Richard Stice, an analyst for Standard & Poor's, who downgraded the stock from hold to sell on Thursday. "There seems to be a disconnect that's developed in terms of some of these metrics. I think it's due for a pullback at this point." "The recent run subsequent to their last earnings report is not based on any news flow," he added. Stice believes his downgrade was warranted because the company is trading above its peer group average on a variety of measures, including price-to-earnings and price-to-sales. The stock has now surpassed Stice's 12-month target price of $30. Standard and Poor's does not have a financial relationship with Plexus. What's more, Plexus' stock is now up over 50% this year, Stice says, a growth percentage way above any of the other primary players in the sector, like Benchmark Electronics ( BHE) Celestica ( CLS), Flextronics ( FLEX), Jabil Circuit ( JBL), Sanmina-SCI ( SANM) and Solectron ( SLR). "I think it is a bit rich at this point," agrees Carter Shoop, an analyst with Deutsche Bank Securities, who reiterated a sell rating for the stock in a Jan. 26 note. He has a price target of $22 on the stock. Neither Shoop nor his firm owns shares of Plexus.