I hope this is ok posted here. I can go into more detail and post pics if needed. I've got an 02 z71 Tahoe that suddenly lost first and 4th. Fluid was perfect but had 5 or 6 codes for solenoids and electrical issues for transmission. Replaced both shift solenoids and no change. Finally figured out the fuse for power to transmission was in drivers fusebox as Ign 0. It was fine. Decided to check for voltage with key on and it was 0. Traced it back to ignition switch and found a little white wire broken loose from switch. I disconnected my battery, removed switch, and soldered the wire back to its pad. Been going strong since. Its almost like it's better than before because it had to have been ready to break and probably wasn't getting full voltage or I'm just happy to have 4 forward gears again. So if you've lost 1st for no apparent reason,check for voltage to Ign 0 fuse inside cab. If 12v it's something else but if 0 find that wire and save yourself a lot of money and time. New switch was $157 if I didn't fix it. If this helps 1 person that's enough for me. Any questions just message me and I'll help if I can.