Ok so.. 01 impala with 133k has the 3800.. Upon start up for like the first 30 seconds it's puttering like it's almost out of gas.. But then it straightens up and all is fine.. I get about 200-300 rpm flex during idle after the puttering is over.. I have not been able to get to a pressure gauge yet to check pressure but.. It's weird that I have no cels and the puttering issue stops after 30 seconds and I only have an issue after that when I'm in WOT.. ideas?