Transmission issues?

[N-ply]

I have an '87 automatic that recently has developed an issue. During driving it has randomly stayed at a certain speed no matter how hard I pushed the pedal, then randomly jumps to a faster pace. It goes back and forth between slower and faster speeds randomly until I pull over. The first time I experienced this issue it was raining pretty hard and I was driving at relatively low speeds in town. Another time this happened I was driving on a country road and about seven miles in it started again, forcing me to pull over after it just stopped moving. I turned it off and let it sit for ten to twenty minutes and it drove fine the rest of the trip, which was another eight or so miles. I tried putting more fluid +additive in the transmission, but it quickly filled and did not fix the problem. Any ideas what this problem could be and how to fix it? Thanks.

[Jfrahm]

What do the RPMs do when the speed is jumping around?

[944tothefloor]

maybe terrible gas in the tank?
can you describe how it feels when it jumps to a higher speed?
when stuck at a speed, are there any strange noises when you floor it?

[N-ply]

The issue has happened at relatively low rpms, but I'm not sure what the rpms are at when the issue is occurring. I have owned the vehicle for almost a year now and the seller did not mention any issues like this, so I have been putting new fuel in for a while now and doubt much bad gas is left. It feels very lurchy when it randomly goes faster and does not make any noises. It is as if the gas pedal isn't responding.

[Jfrahm]

Your description does not make a lot of sense so I cannot tell if you have a power problem or a slipping transmission or what.

If you do have water in your gas you can get that from the gas station and it does cause intermittent power problems. It can also go away if you stop and the water collects away from the tank pickup. If some fuel additive makes the problem go away like magic, at least for a short time, that can be it. There can be other problems that cause bad running too of course.

If the transmission is slipping then you'd see the RPMs climb but the car not go any faster, it's as simple as that. 'Lurchy' is not typically a trans problem with a non-lockup non overdrive trans.

-Joel.

[jeffrsmith]

Are you sure it is a transmission problem and not an ignition problem?

Bad plug wires and damp conditions can cause a miss which some would describe the same as you are describing.

[Jordanarendt]

dirty/clogged fuel filter? Have you changed it yet?

[N-ply]

Yeah, I'm definitely not sure if it is a trans issue. It's just the first thing that came to mind. All of those suggestions make sense to me so I'll check them all out. Thanks for the info about the RPM's climbing. I'll look for that the next time it happens. I'll also check the fuel filter as well. Thanks guys! If anyone has any new suggestions I'd be glad to hear them.