Hummer Forums - Enthusiast Forum for Hummer Owners

As with any 4 speed auto (really 3 speeds with overdrive) the one underlying problems is that they never seem to know what gear to be in... It might appear that a 5 speed would shift more due to the extra gear but for whatever reason subtle changes, faster or slower, can result in shifting... The difference between 5 speed changes is minor so more often than not a 1 gear change up or down goes unnoticed... With a 4 speed however, with the forth really being an overdrive, at times it is forced to jump 2 gears and it can sound and feel a bit sick... The good news is that the best 4 speed auto ever made was the 700R4 made by GM... Motor heads everywhere have long adapted them to fords and mopars because the amount of torque they can take is about double what any other auto could... That 700R4 is the parent of these transmissions so I would bet you'll find it one of the toughest things on the trucks... The 5 cylinder is most certainly underpowered for this application so it would be very wise to ease up and not ask the truck to do what it just can't do well... It should not slip from 1st to 2nd but it also might not be the tranny that is feeling amiss... If the fluid is at the proper level then operate it at reasonable power levels and try to sort out exactly what it is doing wrong... Hopefully then we might be able to help you more...

P.S. My 4 speed auto tranny in my corvette suffered from the same shifting folly as they all do... In 3rd gear you might get a better feel for how it really shifts but don't run that way long or too fast... Just drive around the city for a few miles and you'll see what I mean...