Having some issues with the over drive on my 98 Suburban, just driving along about 50mph or faster and it will shift into drive and then back into over drive... might drive 10 Miles or more and it works fine..then out off no where it will happen again. I also have a issue with my lights I can't get my running lights to work or my high beam's...all the other lights work fine. Could the light's effect the how the Transmission works..appreciate any info...thanks.

 

Is it throwing any codes?

Initial thoughts would be TPS or ESS.

 

Not showing codes just the check engine light is on, but that's on long before this problem started.

 

Post on thetruckstop.us they have alot of experienced 6.5 specific members there

 

You still need to check the mil light, just because it was on before doesnt mean more throws cant throw in that time. One of the codes in there might have been a ignored warning. As mentioned before sounds like a faulty tps or output speed sensor. At this point there isnt enough information to offer much more than a direction though. Need to know all the codes that are stored first.