Isuzu Repair: 2000 ISUZU TROOPER, poor gas mileage, gas additives

Question
After the engine is hot and mostly at highway speeds it begins to cut out. It levels out and gets me home if I accelerate very gently. After it cools it OK. It is usually fine around the house. It also is getting poor gas mileage. It took a full tank to pull my boat about 225 miles. Towing nothing it been using about 3/4 tank to go 200 miles or about 12 miles to a gallon! Tail pipe is black

Answer
Well Ed, that means your in need of a heavy tune-up, I wold start with spark plugs, gas additives, new air filter, throttle body cleaning, and use a can maybe two of carb cleaner. Use your vacuum hose to allow the carb cleaner to be SLOWLY sucked in to the engine, ALOT of black soot and crap will be blown out your tail pipe, go for a drive and get your engine at operating temperature to clean it out. Your surging and cutting out is due to a clogged filter or your evap sensor is clogged or bad.