4l60e no 3rd 94 Sub

Neighbor up the street has a 94 Suburban 4x2. Tranny was supposed to have been rebuilt 5 years ago. No problems until recently. Get in, put in drive, 1st is good, 2nd is good, most times 3rd will be like neutral. He states that sometimes it will go into 3rd like it is supposed to. I told him it is most likely the clutch pack gone, but he says sometimes it grabs fine. So I say maybe its a bad solenoid. We pull the pan, lots of "dust". I point this out and tell him its not bad, no chunks, no grit/grain, but lots of dust, so probably clutch pack. We pull the valve body, clean it up, looks good. Swap solenoids just for fun. Put it back together, fill it up, same problem. I suggest to bring the tranny to the local rebuilder and get it rebuilt. He wants me to do it, but I haven't rebuilt a tranny in years and would prefer not to mess with it. I will swap it out, but that's as far as I want to go with it. Is there anything else to check out, or should I just stick with my orig plan and just get it rebuilt by a rebuilder? I do have all the tools and equipment necessary, I just haven't rebuilt a tranny in quite a while.

I would agree with you, rebuilding the trans yourself may be a time-consuming nightmare.
There may be some hard parts broken inside, which may be expensive to replace.... so much so that getting a rebuilt unit on exchange may be cheaper.

FWIW you may be able to find a fluid flow diagram for that transmission. It may not be the clutch pack at all. There may be something stuck that is causing the 3rd gear hydraulic fluid pressure to bleed off. However, if the truck has been driven a lot in this condition, the 3rd gear clutch pack may be burned up by now anyways. Possibly even if you do remedy the bleed-off problem the 3rd gear clutch pack is compromised by now anyways.

I have all the stuff here, including the fluid flow diagram. And all the other diagrams for that matter. And a sub to MOD, and Alldata. But I still would prefer he has it rebuilt by someone other then me.
Anyway, the local yard will sell him one for $100, so he wants to go that route. I told him no problem, but before we install it we really should have it checked out by a builder and at the very least have it dyno checked. He agrees, so thats a good thing. I told him with the old one out if he wants we can play with it, but no garantees. And we can take time. At least its an easy swap on a full size 2x.

At the very least, whip the pan off before you buy.