4.3 to 6.0 Swap Complete..Slooow

[RichardLSX]

A while back you all help me out on how to do a swap on my 99 chevy silverado single cab V6. I swapped in a 2000 6.0 with a 4l80e tranny, wiring harness and even the steering column.

NOTE: Truck Is Not TUNED it wasn't necessary since I swapped steering columns

NOTE: My truck has 3.42s and I know the PCM is programmed for 3.73s Could this be the problem??????

What i wanted to know is why would my truck be so slow.
Iv'e been told it needs a tune. "which I should be getting tomorrow BTW"
But mildly modded 4.8s still beat me
Iv'e been beat by mild 4.8s, almost bone stock 5.3s and even 4.3s seem to keep up on 20 rolls.
Its hard to explain how embarrasing and depressing it feels to have wasted 3k+ and still be one of the slowest. LMAO

But on a serious note, any suggestions?