Im new to the site and a first time diesel owner so I'm still learning a lot so bare with me. I have a 92 w250 bone stock other than the fuel pin turned and some minor pump tuning (still working on the "tuning" part). "problem" yester while driving (about 70mph) my speedo started dropping 10-50mph but it seemed to happen more often if my rpms dropped. I have no gages so I have no clue what my rpms were. It has not done it at all since so i just want to know if it can be fixed or is it going out? I have been doing a lot of searching on the problem so please don't bust my ***** about not doing research . Any help would be awesome

 

Was the speedo bouncing at all? The first thing I'd check is the VSS (Vehicle Speed Sensor) which I believe is located on the transfer case on the W series trucks.

 

It was but when it would it would only go down in speed, not up. Is the VSS on outside where I can get to it? And another problem I've had is my revers lights stay no matter what gear I'm in but it's done that since I got the truck so I just pulled the fuse till I had more time to look into it more, if any one has any suggestions on that I'd appreciate it!