Ford Repair: Loss of power and temperature gauge issue, temperature gauge, catalytic converters

Question
QUESTION: I started noticing some hesitation during acceleration. So I thought that I may have gotten bad gas. I live/work in Guatemala as a missionary so the last time I was in the states I purchased a new thermostat and fuel filter from Advanced Auto. The thermostat was to fix an issue with the engine staying cool 90% of the time except when the air conditioner is on then it spikes pass normal to hot. I replace the fuel filter, air filter, and thermostat this week. However, today the car the temperature gauge is all over the place and the engine seems to how no power going up hill. When I give it gas it seems to want to go but the loss of power is becoming more and more noticeable. Someone suggest getting the radiator professional cleaned/flush and getting the factory Motorcraft thermostat and replace the after market one from Advance Auto.

ANSWER: I don't think the problem is with the thermostat. What is the year make and model?

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QUESTION: Its a 1995 E-350 Econoline Club Wagon v8 5.8L

Answer
If you are not boiling coolant, I would look at the catalytic converters. When it gets dark tonight, look at them. If they are glowing red, they are bad. This can be confirmed with a catalytic converter. Another possibility is a faulty water pump. But that wouldn't explain the loss of power. Are you losing any coolant? Any water in the oil?