It's my understanding that advancing the cam 4 degrees brings the torque and horsepower curves down toward the bottom end, and retarding cam timing pushes them up to the higher RPM ranges. For a truck I would think you would want it advanced. However (there's a "however" here!) It is considered to be inadvisable to mix advancing/retarding the cam with a special grind. The aftermarket cams take into account the timing, so by changing it you are defeating the design of the cam. You need to know what the grind of the LT1 is supposed to do. Personally, I would think it is ground with neutral or retarded timing for higher RPM performance. I think I would set it neutral and drive it a while, then take it back apart and advance it, and see if I like it better.
With that said, I put a 4 degree cam advance and replaced the stock 1:5 rockers with 1:6 on my 5.7 TBI '89, in conjunction with changing the ECM PROM and going to larger exhaust and intake. It took it from dog to nice driver (in a Suburban with 3.08 rear gears). The PROM and the rockers were the only things that I wasn't replacing as maintenance, so with the additional money I spent on an upgraded exhaust and intake instead of stock, I spent maybe $200.00 making this Suburban a much nicer driver. (The low end torque is really nice for towing and it will put you in your seat coming off the line.)
