Help! Bucking and stalling in a 2001 AWD 5speed manual

Hey all!
Needing some serious help with my 3rd Gen Rav. As stated above it's an 01 AWD with a 5 speed manual. Approx 150K miles. Last year it started bucking sometimes when I was driving it, and it would also drop the rpms and stall when I was at a traffic light. Neither of these things happened regularly, they occurred at seemingly random times, though they did seem to happen more when it was warm out. Did notice that using a fuel additive like techron helped some, but it didn't get rid of the problems. We changed out the battery and and alternator, didn't fix the problem. We've taken the car into the dealer and they have come up empty. I noticed on the forums that ECU's can go belly up on this model but that seemed to be on the automatics and can't find much info on the manuals. Any help or thoughts would be greatly appreciated!