No power up hills stutters on flat road

The blazer 4.3 4x4 shifts fine
through all gears. But going up a
hill it boggs down and will shift
down to next lowest gear when it
gets to 1st gear I have to drive With
it racingWith rpm's at 2000. All the
time I'm climbing the hill the rpm's
are up at 2 thousand, will not go
any higher even with pedal to the
floor. Was running great on flat road
now it's acting fuel starved at any
speed.  it's starting to hesitate like
the fuel pump is going bad but it
was replaced 1-2 years a go. I'm
getting 62 Pressure at the fuel rail.
Hand over exhaust has good
pressure no leaks.  Did a scan and
came up with a code for a bad shift
solenoid which is now gone . It
shifts just as smooth as can be. I
also had the transmission rebuilt 3
years a go. I'm at my wits end. Has
new plugs, wires, distrbuter, cap,
catalytic converter, mass airflow
sensor, fuel filter, Any help or
suggestions would be greatly
appreciated. Thanks too all in
advance.
I didn't mention in last post that
even with gas pedal to the floor the
rpm's never go above 2000-2200
even in neutral.pedal to the floor is
2000 rpm's lift up on pedal just a bit
and it will rise to 2200.