Chevy & GMC Vans

Long time reader, first time poster, at least on this board I think.
I amHaving intermittent issues with my 94 SAFARI for about a year now. When it is raining, or is wet outside, My speedo goes south along with me losing D and OD. I also get some trans slip on take off, and have some other weird things happening, like what seems like the converter trying to lock up at low speeds, that only happened once.
When the speedo goes nuts its at a stop or deceling below 15mph. Usually the speedo will go up to 60-70 and stay there for a few seconds and return to zero. If you inch the van forward it jumps back up to 60-70, then returns and so on and on forth.
I know this is an electrical component, I just have nothing to start with as there is no consistency for what causes the problems. Ive had it happen right off the bat in a rain storm, Ive had it happen after driving 40 miles in a monsoon.
Thinking its the speed sensor, I took a garden hose to try and replicate the problem or narrow it down by spraying the sensor and wiring and even the box on the passenger side of the tranny, but could not. I do know I am getting a constant voltage reading TO the sensor when the problem starts (3.5v).
Also, when in colder temps, the problem NEVER happens, almost as if theres a hairline crack in something thats frozen with ice preventing the water from entering.

I have a new sensor I didnt install yet, guess Im looking for some suggestions before I install it as its not cheap, and would like to return it if its not going to help.

Anyone have any insight?

I am still trying to figure out what this might be and it sounds like a loose connection somewhere.
Unless you live in Tuktoyuktuk, one thing for sure is it is unlikely the sending unit is freezing up in cold weather as it is attached to your transmission that normally operates at 250-300 degrees. This would eliminate any icing on the components.
Has it dropped any codes?
Peter

This is a 94 engine light is not on... There a trick to pulling a code via flashing SES light or something?
I was under the assumption the sending unit is away from the majority of the heat way at the back of the tail shaft...
It seems to me, it has to be a component, rather then a loose connection. I did follow the harness as far as I could, loom doesnt seem to be split or melted... Jiggling it, has no effect. What ever it is, its directly related to the speed sensor circuit. The PCM seems to be getting faulty data and thinks Im doing 70 at a stop light.
I would have to guess, I have no D or OD because the PCM is getting incorrect data and doesn't know what to do. IS there a separate box that controls the 2-3, 3-4 shifts? What gives the shift solenoids a signal, the PCM only?

Read the procedure on another post. I ll try to pull a code tomorrow.

Darn, No codes, really hoping to grab some insight on diagnostics here. Its possible that when I killed my battery last week, the codes were cleared. Maybe that helped my cause too?

It is possible that the ECM has gone bad.

That has crossed my mind, but only 1 circuit has gone bad and only intermittent at that so I pretty much scratched that.

that is a 4L60E, correct? I will check a couple things for you tommorow

I talked to a buddy of mine who builds these all day long. If it is not a speed sensor, it is most likely the harness connection.

reccomends;

wrap both speed sensors in foil (known to have problems with electrical and cellular interferance)

clean and inspect the harness and plug on both ends with brake cleaner and pack it with dielectric grease

Thanks for that. Ill check it out. There is only 1 sensor that I know of, in the tail shaft of the tranny. Is there something else Im missing?