Vortec heads flow too much for a TBI, and you went to even better flowing heads. I'd ditch the TBI outright, and if you're doing that, why even bother with a small cam? Go with .500 lift and a moderate duration. Otherwise, why the big heads?
All that said, I went with the following in my '99 Suburban, now going into my '89 Stepside:
350 4-bolt main block, honed, but no overbore
Factory Vortec heads, 062 castings, no porting, no machining
Factory crankshaft
Speed Pro H345DCP flat-top hypereutectic pistons - 9.5:1 compression ratio
Speedway Motors 5140 steel I-beam rods, 5.7", bushed pin
Lunati 20080720, advertised duration 262/270, lift .507/.515
Factory roller lifters, dog bones, and spider assembly
Chevrolet Performance 12499224 LS2/LS6 valvesprings
COMP Cams 787-16 steel valve spring retainers
COMP Cams 648-16 race valve locks
Proform Parts 66914C extruded aluminum roller rocker arms
Video of it running in the Suburban:
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I had it running, but pulled it back out for a minor issue. I have it in the stepside, but I'm waiting on a Vortec fuel pump from RockAuto to get it running. I'm going to fire it up with the TBI adapted onto a Summit dual-plane Vortec manifold, and I'm hoping to get a Holley Sniper system sometime in the near future.
I went with short duration because of the lack of upper-rpm with the Vortec heads, but that's not an issue with your heads. However, being a heavy truck with big tires, you'll probably want to keep a short-ish duration.