The truck is running rich

What is litre size of engine? Check cylinder compression, see if engine is in good mechanical condition. 02 sensors are part of a tuneup. Are there any applicable mil codes. You can check those codes, yourself. To check codes, use a jumper wire between the A & B terminals at the datalink connector. Turn key just till the dash lites come on, no further. Then the mil on the dash starts flashing, you count the flashes to get the codes. Your looking for two digit codes. Let us know what you find.