when going up a hill at 55 seems like tranny is jittery

[neonlights]

i own a 96 gmc jimmy with a 4.3 vortec when i am driving down the road at 55 or i should say after it shifts into overdrive it want to keep downshifting i really dont know how to explain other than when ur in overdrive it gets jittery when there is a load on the motor any suggestions will help thank you

 

[03Jimmy]

Change the filter and fluid and add some Lucas trans additive. Works sweet and it's cheap. Works like a charm. I put Lucas treatments in my oil, trans, fuel and power steering and have done for years on every vehicle I've owned. I highly recommend it. Si.