1989 full size 1500 5.7 blazer losing power when going up a hill spidering at take off and then at about 50 to 60 power goes from 60 to 35 up a big hill
Possible fuel pump. Check fuel pump pressure after replacing the fuel filter, it should be 9 to 13 lbs. Possible dirty injectors would need to clean up throttle body and run injection cleaner threw the gas. Timing should be checked, so how about a tune-up?
Just had a tune up about 6 months ago and new fuel pump maybe 2 yeas ago.
It may be a vacuum leak, take some carburetor cleaner and spray around the base gasket of the TBI, and around the mating surface of the intake manifold & head. RPM would pick up if there is a leak. You never know on the fuel pump, if need be I would still check the pressure.