Neutral Gremlin

[Fumes]

I have a 2006 GMC with the LBZ and 6spd Allison, and here is what's happening; I'm driving along at 100 km (65 mph) and all of a sudden the trans goes into neutral, you let off the gas and step on it again it goes back into gear and then everything is ok. It does this off and on, about every 10 miles or so. Other than that the trans is working normal. This is at normal operating temperatures. I have had the codes P0700 and once P0502 appear occasionally but not always. :confused:

[rapidoxidationman]

When's the last time you changed the external filter and did a drain/fill service on the transmission? Did you check the fluid level of the transmission (hot, level, in park)?

[Fumes]

Here is an update, first I don't drive the truck everyday but I had it out today to try a few things, it drops into neutral when it's in 4th gear, 5th gear or 6th gear. Also whether it's in 2 wheel drive or 4 (high) drive. But when you go to manual and shift it manually everything works normally.

I have to take the truck somewhere to have any TCM codes, maybe it will tell me something.

[Fumes]

No codes, oil is good, took it to an authorized Allison dealer, they replaced the 3 sets of twisted pair wires for the speed sensors (from the senors to the TCM).

They pulled out the rear speed sensor as when they had the computer hooked up to it was reading that the truck was moving and it wasn't. There were some scratches, marks on it, so they looked a little further and there was only maybe 5 or 6 oz. of oil in the transfer case, (no sign of any leaks either). So they suggested that the transfer case needs replacing as something is moving around in it.

So this is where I'm at now. :confused:

[Kennedy]

Sounds like transfer case pump rub.

Refill and see what happens. Watch for leaks.

[CoyleJR]

Look at the floor above the front U-joint at the back of the TC. If the floor is wet and the TC and everything else is dry you could be leaking TC fluid out of the back of the TC/U-joint yoke. My 2006 leaked through the back of the yoke just in front of the U-joint. There is a flat plug pressed into the back of the yoke and the leak was between the plug and the yoke. I cleaned and sanded it, then sealed it with JB Weld 100K miles ago and no leaks since then. I agree with Kennedy, refill and look for a leak.
Good luck