Tow vehicle, 98 Chevy 3500HD, 454 gas engine with automatic transmission. Drove it a couple days ago and wouldn't shift out of 1st gear. Parked and used my other truck. drove it later in the day and was fine. Drove it again yesterday and same thing, 1st gear only. I don't have much time to mess with it myself, so took to transmission shop. After looking at it, he doesn't see anything obvious. Fluid is fine and nothing abnormal in pan. He's going to pull the valve body and clean things up and check for anything out of whack tomorrow. Looking for input on anything to look for. Truck was parked for about a year until recently and only has about 100 miles since un-retiring it, so I'm curious if that could have anything to do with this as well.

Thanks in advance..

Have you scanned for codes? If nothing wrong in transmission, then you need to look at the wiring. You would not believe how often vehicles come into my transmission shop with wires that have been melted, chaffed, chewed by rodents or connectors corroded.

Good chance its a speed sensor.

Tranny shop scanned codes and didn't get anything there. I'll Get together with him about going over the wiring and any speed sensors. Hopefully he has already been looking into those areas. Thanks guys.

If the fluid looks good my money is on electrical. Check the harness that passes through the side of the transmission. Mine didn't give me any problems but I caught it early. The connector leaks fluid into the wire harness. Disconnect the plug and see if there is fluid in the connector.

VSS won't necessarily throw a code. I had a 4L80e that did exactly what you speak of. Worse when it was cold.

My old 97 2500 suburban use to do it.Replaced the shift solenoids and solved the problem...