Losing power on hills

No
not if you drive it accordingly
steep hills are best negotiated in low fears with plenty of rpm applied
for example on a steep grade with a manual 1st or 2nd or possibly 3rd and the rpm around 2000 constant will cause it no harm
automatics will go to first automatically so keep the rpm at that mark
engine damage is experienced when the gear selected is too high and the engine is placed under extreme load so down shift to allow the engine to work easily
When going down hill select first and only use the brakes to maintain the 2000 rpm range and allow the engine compression to hold the car speed back
the rule of thumb for experienced drivers is this
you select the same gear to go down that it took to come up

If it has lots of miles on it, check cam senor, when was its last fuel filter change/ Has this vehicle been sitting for more than a month?

It is really your choice but your 4Runner is capable of allot more miles with good maintenance. If your looking to save money the V8 4Runner in not a good option.

You need to change trans fluid on all vehicles every 30,000 miles or two years.
Same on power steering fluid.
Spark plugs every 50 to 60,000 miles or three years
Brake fluid every year,not more than two


There haven't been Tune-ups in 25 years --everything is done with computer/processors

That is called Preventative Maintainance

if over 90,000 miles may need timing belt and yes fuel filter can cause powerloss on hill if idiling is irradic check timing

Have you had fuel pressure tested, and/or filter changed. Have you checked for plugged exhaust, such as catalytic converter? Quite often engine will also run a little hotter than normal when exhaust is plugged.

Sounds like a bad plug wire or coil.

Did you check the plug gap on the new plugs? Did you also replace spark plug wires? The stock ones are ok, but typically replacing them with a decent aftermarket wire (along with the plugs) makes a world of difference.

change fuel grade.if that dont do it. i reccamend a tune up

Replace platinum plugs every 60,000 miles, replace iridium plugs every 100,000 miles; replace the timing belt every 90,000 miles.