1992 4-Runner Automatic Transmission Problems

I've been having trouble with my transmission for a few weeks now. I've had it at my mechanic's place a couple of times now, but we've yet to determine what's wrong because it never messes up while he's got it. Whenever he takes it out for test drives it drives just fine.

The problem is very sporadic. It might drive for 5 days with no problem then act up while I'm driving down the highway, or it might act up immediately trying to pull out of the driveway. What happens is the speedometer starts jumping around like crazy and the transmission goes nuts. The speedometer will jump back and forth from 0-60 over and over and the transmission slips. It's as if the transmission is in neutral all of a sudden with high revs and it won't go. I can let off the gas then gas it again and it might catch a gear and go or it might do nothing and still seem to be in neutral. I picked up the vehicle Wednesday and drove it to work and back just fine until tonight. I was driving down the highway tonight and when I hit 60mph the speedometer started jumping back and forth between 60mph and 65mph very quickly and the transmission started acting up. I pulled over in a turn lane and started down a back road. When I pulled out, the transmission was stuck in 1st gear and would not shift. I drove very slowly keeping the RPMs below 3000 until I could pull over in a parking lot. I turned the truck off and waited a few seconds. After starting it up, it drove just fine the next couple of miles home.

I'm thinking I have an electrical problem, but not sure. When this problem first started there was a clicking noise coming from below the shifter. You could hear it click while idling and with the key in the on position without the engine running. I haven't heard the clicking noise since picking up the vehicle this week. Also, about a month before this problem started I had to start using the "shift over-ride" button to shift from Park to Drive.

I did a drain and refill of the fluid the day after this problem first happened and had it flushed shortly after. A couple of people have told me that it might be the transmission filter and that dropping the pan and changing the filter should be done, but I feel like it's an electrical/sensor/etc. problem.

Any ideas?

By the way, the truck has 107,000 actual miles and has never towed anything heavy.

EDIT: Not sure if this is relevant, but the speedometer started messing up over a year ago. Sometimes it works, sometimes it doesn't. I've drove for days with it sitting at 0mph for the last year or so.

 

Update:

Truck has driven just fine since the last incident until yesterday. I pulled out of the driveway and the speedometer started jumping all over the place. I drove approximately 1 mile before the transmission started messing up. I pulled over, turned it off, then started it again. I drove to a store and the transmission acted just fine, but the speedometer never moved. I left it running while in the store. When I pulled out from the store the speedometer was working and has worked ever since then with no transmission problems.

 

is there a lot of miles on it? what color is the fluid? try some tanny conditioner, if the fluid is black and not with metal shavings in it, this should keep it from slipping, and if the problem persists then maybe its electrical

 

I forgot about this thread. I changed the Vehicle Speed Sensor on the transmission the weekend before July 4th. I haven't had any transmission trouble since then. The speedometer still quits every now and then, but no trans problems. I noticed when I removed the old sensor that the little plastic gear/cog was loose and you could spin it with ease. The new sensor doesn't spin nearly as freely.