v6 2 wheel drive 208k mi.

trans will change gears every other second while cruising...like 3rd, 4th, 3rd, 4th...really annoying. and will sometimes start off in 2nd or 3rd gear instead of 1st. sometimes it "forgets" to shift into neutral when i stop and it will stall. and then some days it will shift perfectly fine for hours. when its messing up, if i put the shifter in "1" or "2" it seems to actually do it, but it still hessitates before it shifts. a shop told me they thought it was a short in a wire or a bad shift solinoid. anyone have any other ideas? and where are the shift solinoids on this trans? in the pan? also is the TCM inside of the ECM for this vehicle? or is it that other/smaller module that is under the seat? all that one says is "nissan control module".

thanks