Since chasing down electrical gremlins and seeing a steady 14+ volts on the gauge my trans has been working great for about 3 weeks and a bunch of miles.
Today while backing out of dad's driveway after sitting a few hours, reverse goes away. 5 mile drive home and it stays in 2nd , 2500rpm @ about 40 or so. I get home, still no reverse, and I pull up code 87-High ratio fault. I have never seen this one before.
94 6.5 turbo GMC crew cab 4x4.
Any ideas about what's happening?

I had same thing happen to my transmission, except didn't lose reverse. My positive cable on passenger side battery was a little loose, when I tightened the cable ,transmission went back to shifting normally like it should. I didn't get a ses light when it happened but found code when I scanned for codes. Things like this seem to act up more in winter around here from cold weather, usualy never have problems with it in summer.

Broken piston in the direct clutch drum. Direct clutch applys 3rd and reverse. I will bet you have no 3rd also. Sounds like time for a rebuild.
mike

I had this happen to me once. It was a broken low band, no reverse or 1st gear. This was in a '93. What ever it is Mike is right, rebuild time...

Got the trans re-built.
Ted

I was also getting a code 87 out of mine every couple of weeks. Went to GM and checked the TSB's and low and behold there was one for code 87. It was to replace the PROM chip with an updated one. I installed the chip with my new ECM this week. It hasn't thrown the code yet, but I also haven't driven it alot. But I have noticed a marked improvement in shift quality, and the shifts are much crisper now as well. Plus my torque convertor locks in ALOT quicker and more solid now. The chip was cheap($62 list price) and well worth it.

Lucky you. I hope it holds up for you. I am such a pessemist that I am always waiting for the worst. Stay away from me.

I know mine is going to let loose one of these days. The main reason I did the updated chip was because I needed a new ECM, so I figured I would get an updated chip to hopefully stop the code 87 every couple of weeks. It was a nice bonus to have shifts like the newer 4L80's after updating though. Thought it might be a good upgrade for people who had just had there tranny's rebuilt.

Whats the part # for the chip??
Mine is a 94, wonder if that makes a difference?
Ted

You have to have the 4 letter code off of your existing chip plus all of the vehicle info. Try posting in the TSB section and maybe somebody can post a copy of the tsb with the chip part numbers. I f you get me the code off of your chip and all of the info I can try and get you the part number next week. But there are several different chips.