I don't know too much about cars but my 1988 Ranger is experiencing hesitation/loss of power after driving for about 10/15 minutes. It used to start acting up as soon as it warmed but I replaced the temp switch and now it takes longer for this to happen.

Symptoms-
- Runs great before warm-up
- Loss of power
- Very Slow Acceleration, terrible up-hill
- Engine revs but bogs down more when throttle fully depressed
- Small increase in MPG
- Occasional miss-fire
- Idles fine sometimes/small shake sometimes as well (completely random), stalled once
- Engine Hot, high water temp

What Was Done-
- Oil Change, Replaced Plugs/Wires, Air Filter (no improvement)
- Scanned (no trouble codes or data stream)
- Replaced Coolant Temp Sensor (no improvement)
- Replaced Temp Switch (Takes much longer for car to start acting up from cold start)
- Added Lucas Fuel Treatment (Its possible that I had a dirty/watery tank of gas. This resulted in a slight improvement in power. Same acceleration. Wanted to see if this led to in issue with the injectors)

To Be Done-
- Fuel Filter
- Check/remove the cat

*Note that I had an issue with the coolant system. I used to have to add about a gallon of anti-freeze every two weeks. At random this resolves itself and a month after that, the heater hose burst, leading me to assume that the prior issue was from a small leak in the heater hose.

*Another note that I switched from 93 octane to regular once gas prices spiked. The issue came up during this time period. I returned to 93 octane with little improvement.

*New temp switch reads higher water temp than old one

Sooo I'm thinking there is an issue with with the CAT, Fuel System or Coolant System (only because of temp switch thing)?

 

You have symptoms of a blown head gasket I would check the cooling system with a pressure tester and do a compression test on all the cylinders to rule that out

 

If that's true why would it run perfectly for 10-15 minutes after start-up?

 

I would say cracked head(s) or block ive never had a 2.9 that i didnt have to replace either one of those or the whole dang motor. And all mine started with the coolant disappearing first.