2004 buick rendezvous

So I have a 2004 Buick Rendezvous with 220000
miles on it when I am driving if my RPMs go above
2500 I lose all acceleration if I let up off the pedal
and press the pedal again I can accelerate as long
as I stay under 2500 rpm. I had a mechanic for the
computer to it drove down the road found out the
transmission is Shifting properly in all the gears.
When I get on a highway as long as I stay under
2500 rpm I can get the vehicle up to 80 to 90 miles
per hour but as soon as I hit the gas pedal and the
RPMs exceed 2500 I can hold that pedal to the
floor the engine doesn't accelerate it seems like
the vehicle is not getting gas once I hit 2500 rpm
like I said as long as I stay under 2500 rpm I can
drive the vehicle with no problems every gear shifts
with no issues please help