Twin Screw Blower... TVS1900 or so.
Your not going to get more low end torque from a cam that is larger than stock in a 4.8.
I just dynoed a stock 2003 4.8 the other day. 2000rpms it made something around 220ftlb tq and 89hp. Going up in cam size will only shift the hp/tq curve up further into the rpms not lower rpms.

 

A better question would be: how many pickles can you pull out of a frog's ***?
Or,
How many pancakes does it take to shingle a roof? (Purple, snakes don't have armpits)....... (It's not my fault you're not on shrooms or cid).

Go start your own thread, but a cam won't. Your closest options are swapping to 5.3 internals, a 6.0 swap, FI, or 4.11 gears. There is no cam, and there is no easy or cheap answer.

 

It has the potential to be thrown away and replaced with something better, with very little effort required

Fugheddaboutit

The real little "truck torque" cams, 206° absolute max on the intake, are the only ones that won't hurt it too much. 200° would probably be better. A small motor like that doesn't max out the exh port flow, therefore doesn't need much, if any, duration split. A tight LSA like 110° will help. Don't expect miracles

 

Like RB04Av said, either BTR Truck Torque or SUM-8727R1,