Hi, I'm new to this site but am a member to many others - FTE, GM, Camaro5, Allpar, and Mazda. Hopefully I can find someone who is familiar with the tranny found in the 1996 Tahoe 4WD 5.7l. The other day my son was driving to my house and lost 3rd and 4th and continued on a couple of miles to my house at 45mph or less. He had been planning to do a routine filter change to begin with so we dropped the pan and found the fluid dark and I think it was on the verge of being burnt. After changing the filter (the pan magnet was covered with fines but that might just be with normal wear) and replacing the fluid along with adding a bottle of Lucas stop-slip or whatever it's called, he got it to go into 3rd but still has no 4th. After he talked to some friends who had similar problems and watching some videos on YouTube, he was told and saw that the problem might be a brake sensor or one of the two solenoids on the valve body above the pan. He said there was one solenoid for first and second and one four third and fourth but to me it would appear that if the one for third or fourth was bad, he wouldn't have either speed. He put my Innova scanner on it yesterday when I was at work and found a code was thrown for transmission slippage but didn't give me a number. There's 300K+ on the vehicle and the tranny was rebuilt by a shop over 100K ago. Any suggestions? Thanks.