My 700R4 has developed an issue. It upshifts fine from 1st to 4th, but it won't downshift when I give it gas while driving. If I hit the gas while driving, the engine bogs down, struggles, backfires... No downshift. If I use the brakes and come to a stop, it is back in 1st gear. Upon acceleration, it goes up through the gears fine again. From what I have read, this seems to point to a TV issue. It was working OK before. Phoenix transmission, installed by Bruce's Rod Shop. First one I bought broke, so Bruce's got me another under warranty and installed it. It worked OK for a while, now this... Any thoughts/guesses? Truck is for sale - really need to get this fixed ASAP.