Loses Power While Accelerating

I have a 1998 Jeep Wrangler Sport. I bought it three months ago. It rans rough and lost power all under acceleration. No check engine warnings appeared. I changed the plugs, plug wires, distributor cap and rotor. It ran better, but still low power under acceleration. I check the fuel pump pressure: it held 45-48 psi. The vehicle has always idled perfectly. It does not stall or knock. I put at least three bottles of fuel injector cleaner in the system: SeaFoam.

While idleing, I disconnected each fuel injector just to look for a difference: all made the idle the same amount of roughness. I disconnected the throttle position sensor: the engine stalled and the check engine came on as expected.

The check engine light turned off the next day. But, I had the computer checked and no warning codes appeared, accept for the throttle positioning sensor which I purposely triggered to make sure the check engine light worked.

The engine still loses power while accelerating. If I back off the gas, the engine smoothes out. At 65-70 mph, any hill is an issue. I have to floor the gas just to keep moving and I have to forget using fifth gear.

What should I check next? Thank you for your assistance in advance.