what weight oil should i use for a t3 off road truck? so far i have used 40,35,30,25 and none seam to do the trick. the track i RACE ON is mostly smoth, but there are some good size jumps and bumps.

I would start with silver springs in the front with 35 weight oil and green springs in the back with 30 weight oil.

thanx hank i will try that setup!!!

for me, it be silver in front or greens all the way around with 35/40 with a little lower on the ride height. balance it out so the front doesnt dig in during the big jumps (you can always gun the throttle to bring the front nose up before the jump if your suspension is a bit too soft).

work it from there. also check out what the locals are using, ask around, and see what works for them too.

make sure you bleed the shocks correctly, because air or pockets of too much air in your shocks react almost like not having anything in there to begin with.

i would try greens and 32.5 or 30.5 on smooth tracks thats the best i have found

Everyone can tell you what oil, spring and piston combination to use... but if you do not know what will result from those changes or why they might be changing things, you will not learn anything.
Do some research and see what spring rate, Viscosity, and pack mean and how they effect the handling of your vehicle.
THEN.... take the advise of these experienced racers who have shared their set ups with you. Compare and keep notes to help you remember what the changes were and how the effected you vehicles handling.
RC101 on this site is a good place to start.
Dan