hey guys not sure which trans i have. think it is a 5 spd but not sure. i read some where that only 6 spd came on 06's but my dads 01 is got one i think. his truck hauled when he first got it when it was stock now he has a programmer and it ripps. my truck is an 04.5 gmc sierra 4wd. vin is as follows 1GTHK29254E350861. i did try to search but was unable to thanks guys

04.5 came from the factory with a 5 speed.

i know its supposedto be a 5 spd and i think it is. but i can almost gurante my dads lb7 is an 6spd. at 70mph his tach is at 2000 rpm mine is at like 2200-2300rpm. might have tto get a 6spd cause i really like it

With a 5-speed Allison and 265 tires, 2000ish RPM's at 70 MPH is normal.
If the Allison sump temp is below 88 deg F., the torque converter will not lock-up, and you'll see an additional 200-300 RPM's until the TC locks.

Below is a RPM calculator.
In this calculator, the AOD*, (Automatic Overdrive), is adjusted for 0.70. Our Allison is 0.71, which is close.
I calculated 3.73 gears, 31.8" tires (265/75/16E), and 70 MPH and it calculated 1931 RPM's. I'm not sure if the 31.8" tire is adjusted for the true rolling radious or not, but it is close.

http://www.ringpinion.com/Calc_RPM.aspx

Maybe you have a lock-up problem, or you tranny was still cold. Warm it up and recheck your RPM's.

wow cool thanks modified. that was helpful and very informative. On a side note planning a few mods and was wondering the limit of a stock 5spd allison. How much rwhp can i put down safely before cluthing start to slip and i shorten the life of my transmission