randy stanfa

I have an 03 tahoe 4.8 rwd about to go on boost.its about to roll over 240k doesn't skip a beat and tows 5k pounds a day while on 33/12.5/20 it will be getting a 76mm turbo e85 tune until the engine or trans takes a ****. But I'm going to be using this as a learning experience while letting my tuner get the engine right. I have a big bore forged 5.3 bored to a 5.7 gen 4 rods and oversized valves and ported heads ready to go sitting in the shop. But I recently acquired an 03 2500 6.0 4l80e truck that was wrecked but still runs and drives.
i know all three of those engines will handle it but I also have a 6l90 core that's supposedly good . What's going to be the most budget friendly/reliable way I should do this with out crazy fab work. I don't mind doing a budget build on the 6.0 but feel like I should keep that as my next back up just incase.the trans side is really my main concern. What would you do given these options?
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AwesomeAuto

I'd boost the current 4.8 and call it good. I did ~900 wheel on my 240k mile gen 3 4.8.
Skip the 6L90, its a massive hassle.

The 4L80e is an amazing trans.