Truck running ruff once warmed up check engine lite comes on but goes off as soo on 1990 Chevrolet 1500 Pickup

Truck starts running bad after awhile of driving till ya step on accelerator then runs like a champ took air filter off and under side of lid was wet and smelled like gas does not die and only does it ocasonaly and only when you are at crusing speed it has a new fuel tank with new pump just started acting like this poured sea foam in it Friday havnt ran it all out yet but should be out of gas today cause it get no miles per gal :( smells like it is running really rich allmost to the point of burning your eyes

Asked by for the 1990 Chevrolet 1500 Pickup
Coolant temp. SENSOR comes to mind.... not the sender for the gauge in dash... but the sensor for the ecm! Scan test for live sensor data needed, also for map sensor values.