[obzidian]

if im not mistaken, your 03 has a 4l60e 4spd trans. Not a 4l80e.

There is a difference and basically, the 4l60e will not tolerate as much power or torque as the 4l80e. The 4l60e has been known, in the f-body/vette/goat, etc. side to give out under stock power, it is delicate and a bit fussy. The 4l80e, on the other hand, will hold upto 700lbs trq. stock. I have one right now built for my camaro, 408ci turbo, that will hold above 1000hp..

You said you lost 3rd and 4th gear, plus lock-up right? Well, that is a common failure in the 4l60e and its your 3-4 clutch pack. Not enough line pressure or oil, heat, friction, and strong hard wot-type of shifts into 4th are all contributing factors to a failure with teh 3-4 clutch pack.

Now, good news is that you can rebuild it stronger than stock and it should hold, SHOULD. ME, i would go with a 4l80e. The only downside is that you will have to search for misc. parts to complete the install. The bolt pattern whould bolt right up, however, you might need to modify your crossmember, maybe not. TCI has a computer controller for the 80e that controls the shifts, line pressure, TClock-up, etc. of the 80e so that is easily taken care of. A different driveshaft yoke or driveshaft might be needed.

I know it sounds like alot but inreality, these trucks are massive and i has a bit surprised that they didn;t come with a 80e. NO big deal, really, for hte stock power... but as you can see, its a possibility, though it could be avoided.

rossler builds some great trans. Also, try FLT, finish line performance, they have a 4l80e that should be what you need. they have one, parish, that holds over 1000rwhp with a 408ci t88 silverado.

good luck, i'll see if i can find more info on the swap or the 80e. I know im VERY new here, this being my first post!!! BUT, i have been dealing with these trans for over 5 yrs now, reduild three 4l60e's and now on my first 4l80e.. the 80e will hold, just got to get to fit which isn;t a problem at all really..

good luck!!