Power issues - hesitant performance

my sister has a 97 4runner, 3.6L and has been having running issues for some time now

over the past year the following has been replaced:

- cat
- plugs
- all coils (was throwing codes)
- MAF has been cleaned (this weekend)
- fuel filter (this weekend)

originally the car was just seeming gutless...going up a steep hill on the highway the truck would accelerate to about 80 then stop accelerating but the rpm's would continue to climb

after this weekends work, it how does it a 90, but the tranny downshift pretty violently and continues to speed up then upshift

any ideas what could be causing this? bad 02? TPS?

the plugs were changed last year so they could have been fouled out again

any help would be great.....she'd getting terrible fuel mileage in the process and she drives quite a bit

thanks