If your talking about the 4.3L i have the same engine and I do 100 miles a day on the highway. Th 4.3's never really had much in the top end. Yours is doing and acting exactly the same way mine is. Mine does the same exact thing. 4.3l's arnt know for having much in the top end. But they have a lot of torque in the lower end. Ive asked around and did some research about it and some have said that it could be that the injectors in the TB are either worn out or clogged. Im going to be rebuilding my TB with new gaskets and stuff. Im gonna try to reuse the same injectors. If anything try using seafoam in the gas or techron fuel cleaner. I work at a parts store and everyone ive talked to say the techron in the best stuff along with seafoam. I noticed that once I get to almost 3000 RPM it suddenly acts like it got a big boost of power but it seems to lag or lose power around 2000 rpm. mine has over 230k miles on it now so its expected to lose power but still it could be something simple. Ive heard that advancing the timing a little bit helps but im not much of one to play around with the timing so i dont know if it works for sure.
Good luck! Let me know what you find out
Good luck! Let me know what you find out
