I have a 97 c1500 5.0 vortec it has weak acceleration, poor idle, and horrible mpg. Ive replaced a lot on this engine including all ignition except for the distrutor, and upgraded the injectors to mfi. Still feels the same. Once in a while it will feel better like it has good power again, but usually only after it sits for a day or two. My MAF seems to be working properly, about 5-6g at idle and when I accelerated up a hill at 2k it went up to 78g. I unplugged the maf while it was running and nothing changed at all. I thought maybe a vacuum leak but i dont know how to start with checking for one, and if it was a vacuum leak its not like it would be from pulling the upper intake because the truck had the same power before and after. I could really use some help