Hello,

I'm a member on a bunch of forums and have been browsing here for a while. I currently have a Chevy GMT900 RCSB 4WD that I am turning into a prerunner style that I want to mod. I don't even know where to start to be honest. I'm not liking how everyone says the transmission (4L60E), transfer case, and diffs aren't very tough on this truck.

However, I want to get a slightly lowered street truck to use as a daily driver and am not sure what I should do. I like the looks of the new GMCs but don't know what would be better for a drive train 2WD, 4WD, AWD... Probably another RCSB.

Thanks,

Dustin

 

The 4-speed auto is a 4L70E in the GMT900 chassis (might be wrong on that though), which has multiple improvements over the 4L60E it replaced. Combined with the Dex-VI fluid, it makes for a decently strong transmission. My Dad tows with his 09 Sierra 1500 Z71 all the time and it still shifts like a champ behind the very fun aluminum 5.3L in it.

The whole truck should have no trouble with some mild offroading and 35" tires, but that depends on your direction with the prerunner angle. You can go with a Fox replacement shocks, bushwacker cutout flares and 35's for the look and near SVT Raptor performance or you can pony up for a mid or long-travel suspension and really turn it into a prerunner.

If you are leaning closer to the second scenario, than I would want to upgrade to a 4L80E or something, along with a trussed 14Bolt axle and stay away from 4WD.

 

I wanted to add, for reference, that my Dad's 09 Sierra has 100,000miles on it and I broke one of the rear leafs and an axle seal, while Dad tows 3000-8500lbs with it a couple times a week.

So the 4L70E has lived a harsh life, but still works great.

 

Thanks for the reply. How can I tell if my transmission is a 4L70E (built April 2009)?

I am wanting to go up to 35" tires on 17X9s, front fiberglass fenders, and mid travel suspension (BMS or ReadyLIFT). I know 2WD would be a lot easier but I would like to keep it 4WD if possible. Is there anything I can do to upgrade the front diff? I don't think lockers aren't available for the 8.25" (and that it probably couldn't handle it if they were).

 

These transfer cases are strong as hell

 

That's good to hear. Do you know what model number my truck has in it or how I could find out?

 

The GMT 900 came with 4l60E's. (4 speed) The 09+ 5.3 came with 6l80e.(6 speed) easiest way to tell is to look at your rpo codes in the glovebox or drive it. if it shifts 4 times u know u have the 60e if its an 09+ and it shifts 6 times then bam. As far as trannies, there is a hit or miss on the 60e. I swapped mine out for an 80e to be safe. The transfer case should hold up fine. To be honest, if u have a 60e go to an 80e. for ur rear end do a truetrac. and for you second question I would say a RCSB. i drive my truck daily. its a crewcab 4.8 n i love the setup. Stick with the 4wd so u can launch at the stop light. throw a converter, tranny cooler in there and a shift kit on the 80e and ull be good. for a reasonalbe budget u can do cam gears converter tune and a drop. the truck will be plenty fast and meet all ur needs. im sure others will chime in but this is my .02 and should give u a good start

 

I know I have a 4 speed, I just didn't know if it was the upgraded 65 or 70. From my researching, over about 500 HP a 4L80E will be required. It sounds like I can get away with what I have for a while then.

The only cons to 2WD would be a loose rear end and lower resale value, right? I am considering 2WD for the lower weight, fewer parts, easier to mod front suspension, and 1 less diff to swap out gears in.

 

good choice. then go off ur rpo coeds in glove box if its an M30 then its a 60e 803 is mt1 if i am not mistaken, ill have to double check

 

It says M30 so I have a 4L60E. I guess we'll see how long it lasts!

If anyone has any advice or any articles on 2WD vs 4WD vs AWD for a street truck it would be appreciated.