Speedo not working, AC not working, ABS, Brake and check engine light on?

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I have a 2001 Dodge Ram 3500 Van and about 9 months ago the speedo stopped working, the AC stopped working (blowing cold and vent blowing on HIGH), the ABS and Brake light came on steady and the check engine light came on. It also pulsed or surged at times when driving. I had it hooked up to a computer and the code read P0500 "no vehicle signal". So I replaced the rear speed sensor and it did not fix the problem. The fuses were all fine. I had it in a garage for almost a month as they checked wires and hooked computers to it to no avail. I started reading posts and saw that it could have been the ABS Module. So I found a great company online (ModuleMaster) out of Moscow, ID and they rebuilt my module for $130 and sent it back to me. When I got it back I re-installed it and all of the problems when completely away. This lasted for about 9 months. Sad to say the same symptoms are back and so I called ModuleMaster and told them what it was doing and they told me that they would gladly look at it again (since it was under a 5 year warranty). I sent it off to them and they re-worked it and when I got it back the paperwork said they "replaced wheel speed signal conditioning chip and reflow soldered everything again". I reinstalled it and voila everything worked again with no problems ...until I put it into drive. Once in drive the ABS light, brake light, AC stopped working, etc. Back to square one. I am at a total loss as to what is causing this problem. Can anyone help me with this? I don't really feel like taking it to the dealer as it will cost around $1,000 if it needs a new ABS module and I am not totally convinced that's the problem. It seems like the second it hit R (reverse) as I was putting it into drive everything started up again. Of course this might not mean anything at all. Also, at times when this has happened in the past the reverse lights don't work. Something wacky is definitely going on and I would like to get to the bottom of it. PLEASE ADVISE! Thanks! In case it helps, I have also had times when the AC/Heat switch would not work (blow at any speed) and I replaced a small part that goes into the blower housing. Not sure if that could be related to the problem or not?...