Maybe someone is still around on this post to answer a question. My GV is auto shifting almost right away, it used to wait till around 55 mph to shift. Any ideas? By the way great resource, glad I joined...
You are in Riverside and Gearvendor is headquartered near San Diego. They have decent customer service and will answer your questions. Since you are close, they could even take a look at it.
If you are deadset on solving this on your own (for $ reasons), then your controller is having an issue. My
GV and controller was used (from a junkyard) and after a few hundred miles, it burned out. Aside from resoldering components in the old controller, there wasn't much I could do.
But if yours is shifting early, maybe the speedocable sensors are worn or damaged. Check all your wiring for anything suspicious or any connectors that are loose. If everything looks good, then take all the connectors apart and check for corrosion. I apply dipole grease on all my connectors after I clean them out with electrical connector cleaner spray. This prevents further corrosion as well as lubricate the delicate connectors after decades of use and brittle plastic.
If after all that, you'll need to ask GV HQ for more info. I ended up scrapping my controller and put an OD switch on the dash. Whenever I wanted an Overdrive (like around 55mph), I just manually turn on the switch. It's just a 12v connection to the solenoid on the drivers side of the OD unit, and an inline fuse.
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You can see the red wires (with the blue connectors) i used to bypass the controller at the solenoid. Works ok for me. Aside from stop and go traffic in Los Angeles, the manual switch is not a problem.
Also, as you can see in the image above, I highly recommend the "Maximum Overdrive" brand deep sump for that OD. Much much much bigger oil capacity and ports for a temp sensor. Never had an overheating problem on my IDI GVOD once I put in the Max Overdrive deep sump. Here's my write-up on the M.O. install.:
http://www.nickpisca.com/diesel/engine/gearvender-deep-sump-installation-tutorial-maximum-overdrive/