just wondering if anyone could help me with this question? i got a 1981 GMC jimmy 4" lift 36" tires 4 speed manual transmission. the only way to get moving is in low. cause when you start in 1st it is like starting in 2nd. does my transmission need to be regeared? if you have any info for me that would be great. 350 motor in it.  

It sounds like you need to change the axle gears, not the transmission. what is the ratio you have in there now? with 36-inch tires you'd want at least 4:56 ring and pinion to regain acceptable power. 4.88 or higher would be even better.  

not sure i just picked this truck up i image it would be stock.  

it could have as high as 3.08, 3.41 was a common gear for those in which case it should get up to speed fairly well. still it needs 4.10 gears to be economical with the 1-1 ratio of the 4spd tranny. anything lower will really be humming. @65 the engine will be spinning just shy of 2500rpms (4:10's)....well above what a stock 3.08 geared rig with 30" rubber turns. and they aren't slow...
the 4.88's turn the 36's 2965rpm's @65.
if I remember right the manual has a 2nd gear ratio (1st) of 3.58 so even if it does still have 3.08's it should launch the 36's ok.

first on the th350 is 2.52 and the th700r4 is 3.06

if it had the 700r4 OD tranny I'd agree on the 4.88, or better yet a 5.38.... even the 4.88's would keep the tranny searching for gears pulling a slight incline.
5:38's in OD @65 turn just under 2300rpm and wil help keep the 700 from getting toasted from the big tires.

there should be a tag on the front diff cover with the ratio stamped in it..