Just when it looked as if Tesla Inc.  (TSLA - Get Report) was going to roll over, shares caught a big pop on Monday. With Tuesday's 2.9% pop, shares of Tesla are now up more than 7% this week.

So what's adding to the gains on Tuesday? Speaking on CNBC's "Mad Dash" segment, TheStreet's Jim Cramer pointed out that PepsiCo (PEP - Get Report) -- one of his "absolute favorite stocks" -- placed a preorder for 100 of Tesla's electric semi trucks.

Pepsi joins other high-quality companies like Walmart (WMT - Get Report) and JB Hunt (JBHT - Get Report) in preordering Tesla's new big rig, even though a delivery date is years into the future. The count is now over 250 trucks, which is an impressive number, Cramer acknowledged.

It also makes Tesla a difficult stock to short, he added.

Investors would be wise to think of Tesla as a technology company rather than purely an automaker. With "real companies" like those above placing big preorders, it really says something about the product, explained Cramer, who also manages the Action Alerts PLUS charitable trust portfolio.

This is a lesson on how hard it is to short stocks in the current market. While he does not endorse Tesla either on the long or short side, Cramer did preach caution. "Be careful on the short side," he concluded.

PepsiCo is a holding in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio. Want to be alerted before Cramer buys or sells PEP? Learn more now.

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At the time of publication, Cramer's Action Alerts PLUS had a position in PEP.