I just got an '03 silverado 1500. Has a 4.8L V8..

I'm kinda curious sometimes when going at a speed of say 40-50 sometimes I'll punch the gas and it'll downshift but only to 3K RPM. And give me no power until the rpm's come up to speed. Slow as ****.. Is that normal?

Also.. When going at highway speeds (60+) and I punch it.. it downshifts but goes NO WHERE!!! A complete dog!

I got the stock muffler cut off and put a 40 series flowmaster on it. Single in dual out. But no pipes the exhaust dumps out of the muffler.. DO I lose power by haveing it set up like this? Lack of back pressure?

What could I do to fix all this?

I also put in a new kn air filter. Not much but its a start.. well not really...

 

To begin with, everything I have heard about the 4.8 liter is that is a complete dog to begin with

 

What you are fighting is torque management, it retards the timing at more than normal throtle, wide open, I had a similar problem in my 03 5.3, the guys at goodguysgarage.net got me set stright, I can do burnouts and smoke a HEMI any time. Their site is not finished but the phone is 316-258-0358 they answered all my questions and helped to find some I didnt ask, by far the best mod I have made, I have a whole new truck. Hope I helped.