the 5.3 v8 does have a 4t65e but its not the same as our 4t65e/hd's for the 5.3 GM installed a wider chain. 1" iirc so many of these chains have had issues that they are no longer available so any replacement trans are of the weaker design and are doomed to fail. It might be that the 5.3 has too much tq down low and the trans cant take it.

OP: if you are looking for more power i would recommend a 3800 powered car and build it up. would be cheaper then the 5.3 and easier to make power.

 

the transmisson in the ls4 cars is a well documented issues. from what ive seen people that baby the car are the ones that have most of the issues. people that drive them like theyre stolen seem to do fine(myself included). if you buy the car the first two suggested upgrades are a shift kit, and a trans cooler. next would be save up for the tep rebuild. i have yet to see reports of ls4 cars with a tep trans having problems other than high hp na cars or fi cars that are flogged at the track, and even then the gripe is changing the chain every couple of years since the 1" chain is no longer available. the gxp has tapshift and what i assume is a manual valve body that allows the car to take 1st at 40, and hold 2nd through the traps at 100. other than that they should be the same.

 

I take great care of my car, oil changes every 3,000 miles, had the cooling system flush at 32,000, being that i am 55 years of age, i have never, ever, burned rubber from a standstill, as we all know that is not good for any fwd transmission.The only time i push my car is when i am pulling out onto the freeway. Coming back from vacation with my wife & little girl,that is when my trans starting shifting fast & hard. At 32,500 miles, had to drive 485 miles home like that.As i said before the dealer fix that problem but as soon as i pull off there lot this problem of banging into gear from a red light when the car is cold started when i was no more then a few 1000 feet from there dealership. What i do not understand is that i do not drive my car hard, had the monte out 4-6 13 & 4-7-13 in it ran find. But on 4-5-13 it must of bang into gear 5 times that day.I am at a lost on this.

 

I have an '07 GXP, and I really like it. Hasn't given me any problems so far (other than having to change the battery which is really a pain- but that's just normal wear and tear). Granted I've only got about 25k miles on it (owned it since ~2500 miles/2years old). Only real mods I've done are an intake, and exhaust cutout.

The car I traded in for it was a 99 GTP with a basic bolt on setup- would've made just about the same power as the GXP, maybe a tad less. Drag race wise, they would be about dead even, at least in the 1/4. But for daily driving, I like the GXP so much better. With the low compression, low final drive, and small engine- the GTP was a bit of a dog driving around- you had to get it into boost before it really felt any kind of kick. With the GXP, there is just tons of torque down low that you can pass cars on the highway without much extra throttle and without revving it way up.

Don't get me wrong- I love the 3800's, but if you're just looking for a DD with some decent grunt- the LS4 is pretty nice. I guess if I had all kinds of issues like some of the people do- I wouldn't be as happy- but overall I'm not hard on the car at all either.

 

Great answers guys, I appreciate everyone and if I could give points, you'd all get them. I really dont like the boost cars, my friends feels as if it lags a bit before a boost even kicks in.

And lol I would drive my v8 like it got stolen sometimes. My 3500 likes to lag a bit when shifting, usually when it does that, I'll just push it a bit harder and it clears it right up. If it does it while its cold or im idle, i'll rev it till about 3.5 and let it idle then take off as usual at a light. My 3500 tranny isnt perfect and it has its lags here and theres, but I do think pushing it like a mad man sometimes opens it up. Just imo lol