OK, I know this has probably been gone through before but I'm new here and don't have time to go through all the posts. I have a 2003 Suburban 2500 with a 6.0. It has 158,000 miles on it. When the truck is cold or after a retart where it has sat for an hour or so when I start going and the truck shifts from first to second I have no acceleration until I give it more gas then it will down shift and speed up and then shift through the gears fine. It is not a tranny issue. I thought maybe I had plugged cats but with a back pressure test both sides are clear. I do not have a check light. I did a fuel pressure test and it was showing at 55 PSI but during accelleration the needle wagged back and forth from 45ish to 60 ish very fast and then would steady out. Also in the last several days while pulling a trailer down the freeway I could feel a hesitation/misfire. My gas mileage is only about 10.5 to 11 mpg mixed use and about 12 freeway....is this normal for a suburban? I have a brother with a 01 silverado 2500 with the 6.0 and he averages 16 ish. Is this a fuel pump issue or something else? THanks for the help.

 

The 45ish is low and could cause the problems you are describing.