TyeeMan

My last truck was a 99 1/2 ton 4.8L with the 4L60E, I had the same problem. No trouble codes were set, so I took the dealers tranny guy for test drive, he brought along his tech 2 scan tool. As we were driving I told him what exactly happened and when. He picked it up on his scan tool right when I said it was going to pop out fo OD. The problem was two fold, part of the problem was the tcc solonoid, the other half of the problem was the port on the valve body where the tcc solonoid seals off. See, the tcc solonoid is sort of a proportioning valve, it has a steel ball that opens and closes and that steel ball seals off on port in the aluminum valve body. See where I'm going here, , steel vs. aluminum? Any way, the steel ball starts to peen away the surface of the aluminum valve body, when the fluid gets warm (that's when mine did it) the fluid thins out some and leaks past this "improper" sealing surface and it messes with the line pressure. The fix - the dealer pulled the vlave body and took it to a machine shop where they reamed out that port, installed a steel insert, so now the steel ball in the tcc solonoid can seal off on steel surface. $450.00 problem solved. Hope that helps.