1991 R2500 suburban 7.4l uphill overdrive drive ability problem

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Hawkeye12

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While driving uphill in od I hear what seems like a rpm change for just a second, it might do this every 5-10 seconds. Any ideas, transmission, misfire. It doesn’t seem to loose power, I just hear a change in how the engine sounds
 
Really hard to say with that amount of information.
I assume you have no codes?
 
No codes. Planning to put in a tachometer Saturday to see if rpm jumps when this happens. First time I heard this I thought trans slip, but then started thinking misfire. Checked distributor cap rotor are good. Checking plugs tomorrow. 135,000 miles
 
Have you checked the transmission fluid level?
Have you ever changed the transmission fluid and filter?
When is the last time it had a basic tuneup?
 
Trans fluid filter changed about 1 year ago. Changing plugs tomorrow (Monday). Cap rotor wires very new. Original coil. Fuel filter maybe 3 years old. Average 5,000 miles a year driving
 
I notice it does same thing in drive( level surface) at 55mph. Could it be something to do with torque converter clutch, lock up solenoid going in and out. Kind of what it feels like. Thanks much. So I think this has nothing to do with hills. In drive happens at 55mph and overdrive at 72-73 mph
 
Yes that does sound like the converter. Have you checked the electrical connections to the transmission/converter?
 
Not yet. Do I just look for any wire connections coming out of trans. Was reading about speed sensor( could that be it). Tranny shop can’t look at it for 3weeks. I’ll check underneath at trans after work (Wednesday). Suburban drives strong, I just notice those little changes at those speeds. Hope it’s not a serious trans rebuild. Thanks much for ideas
 
Vehicle speed sensor usually shows a speedometer problem also.
 
Speedometer works normal. Do you think it’s internal( needing rebuilt)?
 
You stated the transmission fluid was changed a year ago, was the filter replaced at the same time?
You dont appear to have slippage so I doubt you need a rebuild.
This is a general link on the topic that does not have specifics for your vehicle

Testing the Lock-up Torque Converter

prod.lv2014.gener8cms.net prod.lv2014.gener8cms.net
 
Thanks for the link testing procedure. I’ll check that tonight. I had a hard shifting problem year ago( trans shop found bad computer voltages)replaced with used computer also changed fluid, filter. Probably 3-4 years ago I changed out fluid and added a extra trans cooler and external trans filter. Ordered and changing external filter Friday. This transmission is maybe 16 years old. Original went bad at 68,000. Had a shop put new transmission from chev dealer 2004. So this trans has about 70,000 miles on it. Thanks so much taking time helping
 
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