Car doesnt accelerate on a hill at 60 mph

What is your question?

While driving on a hill at 60 mph and 2000 RPM my car stops accelerating and the gas peddle stops working. Same at lower speeds if I try to punch it. Timing belt replaced 25,000 miles ago. No other issues. Runs great. Tried putting fuel addatitive to clean injectors. Didn't help. Don't think its the fuel pump since it only happens when there is s load on the engine. Maybe timing belt? However it was changed more than two years ago at 105,000 miles. I don't have a trusted mechanic in the area. Hopefully you can help.

What makes this problem better or worse?

Its better when I let the RPMs drop

How long has your 1994 Lexus LS400 had this problem?

Two weeks