Im using 4 energizer lithium batteries at the moment and seem to have cured the probs i had with the mg995.
I have had about 3 bashing sessions at 2 hours a piece with no probs.But i do keep the car indoors (keep them warm).
Bit off a stange one but if your car is set up right the trim during running should be set at the bottom
Ps.You can adjust your trims on the radio,thats what they are there for.
All i can sugest is ellimination,but to do that you need spare radio gear or a good m8 to lend you stuff.
First of check the reciever switch then batteries + pack,reciever,transmiter.