I have a 97 Chevy 1/2 ton 350 vortec auto. Runs great when cold but when I plow with it for three hours or so I start to lose power. I'll push snow into a snow bank and when I try to back up in 4 hi it won't rev up or spin a tire or anything no matter how much pedal I give it. In fact the more pedal the worse it sounds. Has a howling growl, a slight misfire and ping. I can smell coolant but that's probably bc the rubber nipple on the radiator sprayed the engine a bit ago. Anyways, when I go to take of dis the road I will go fine unless I get in to it a bit harder and that's when it'll start to fall on its face again slightly pinging. New parts include..... New cats bc my old cars rotted at the flange, new fuel filter, checked fuel pressure it's ok, plugs, wires, cap, dizzy, went to replace spider but previous owner already upgraded it. Could this be a bad coil? The repair shop couldn't find anything so they told me to bring it to a transmission shop. The transmission guy "thinks" it could be either a bad torque converter, clogged exhaust, or something electrical in the tranny. Btw it runs great when cold and if you fire it up it will idle all day like its nothing. But when it is used for a couple hours something gets warm and holds the truck back and robs my power