Look, I know this may sound a little odd. Given the fact that Red John is somewhat lanky and has a very calming voice (season 2 finale), and we know that Gale is nowhere close to that; but hear me out.
Let's start with the season 3 finale. The team was investigating the Todd Johnson murder so that they would figure out the mole. Who were the suspects? La Roche, Adilles, Bertram, the CBI reporter and Craig O'laughlin. I don't know if there were others but the fact is that of the 7 RJ suspects, Gale Bertram is the only one who's on both lists. Sure, Craig was the guilty one but that doesn't mean Gale was entirely innocent. 
How would you explain RJ foiling what seemed like a perfect plan? What Jane failed to consider in his plan is that the people connected to RJ could be more than one. Imagine this for a minute. Craig receives a tip that Hightower was in room 505, then tells his "boss" (Gale/RJ) about it; On the other hand, Gale will be like 'Hey, but I thought she was in room 605'. I mean, won't Gale know that something's up? Come to think of it, How else would Red John know what Jane was planning?
Which brings me to the mall incident. Timothy Carter (another disciple of RJ) was there purposely to meet Jane - you know, because Red John kindly asked him to. How many people were supposed to know that Jane was meeting Bertram in the mall?Well, it was Lisbon's team and Bertram. So how did Red John know about the meeting? Maybe I'm missing something here but Jane has a good reason to suspect Gale Bertram. 
Gale is also kind of fishy, he works closely with Bob Kirkland regarding the PJ/RJ situation and we know that Kirkland isn't exactly the nicest of guys. Then again, he isn't very good at poker and Jane has tricked him quite easily and Red John doesn't seem to be the type that would be tricked a few times.