Forgive me... I do not remember...

But have you tested for good connections at the transmission case electrical connector?
12v Positive and 12v Negative.

Proper grounding via a heavy gauge cable from the battery directly to the engine cylinder-block/ transmission is very important.
Only using tiny ground straps to the engine/ transmission is not sufficient.

Once you have confirmed power and ground connections...
Proceed with continuity testing from the case electrical connector terminals (one at a times) to the PCM connector terminals.

 

I did not do any testing of the wires. So I will bet anything that the trans shop finds nothing wrong with the transmission, so I will be spending more money to not have it run.
Why is it so difficult to find a good mechanic near you, unless you have lived in one place for a while and almost always have car trouble?

 

Honestly the profession of the Auto-Technician is a broken trade...

The people in this trade are never appreciated, treated like idiots, payed horribly... and then thrown into a field with some greedy business owners that only care about the bottom line!
So the people who now end up in these jobs are miserable and have no work ethic...

The Auto-Technician Profession needs a complete revamping, otherwise it will simply get worse...
and then just die out.

 

Would you work your hardest if you were treated this way?

 

You are right. They are under paid for what they do. It also seems that some places give the whole auto repair industry a bad rap with screwing people over that are not mechanics.
I just want to know that they are diagnosing the problem and not just jumping to the most expensive thing. It could also be the areas that we live in, Northern Virginia is pretty expensive and therefore if a mechanic wants to be in the area they have charge a good amount.
I do not want to take work away from anyone, but when you have gone to a few different shops and still do not have a correctly working truck, I have lost a lot of faith in the shops here. Even when they will not look at something because it may be a bit difficult.

 

I wish you good luck in the diagnosis and repairs needed.

Be grateful that you don't live in the NYC area, like I do...
Hourly rates here for a basic Auto-mechanic start at about $165/ per hour to $225/ per hour for a Dealership starting rate.

 

I am starting to feel badly for you.

There are so many really shitty Auto-Repair businesses, owners, managers, technicians, and mechanics...
I would try and keep us posted on any news of tests and/ or diagnostics completed.

I would like to try and aid you as much as a person can do over the internet (which sadly is not always very much).
Fortunately you do not have an overly complicated project/ vehicle.

You have a General Motors GMT400 K-series 1986 Truck (Jimmy/ Suburban)...
Which had no electronics at all (unless ordered with the CCC E4ME Rochester Quadra-Jet and ECM).
Either way... you are not using any OEM electronics from this era now.

From what you have stated thus far; it sounds like you have"
-A 2000 GM Generation III Small-Block Chrevrolet 6.0L engine (Cast-Iron Block + Cast-Aluminum Heads) Possibly RPO: LQ4.
-A 2000 GM Power-Train/ Hydra-Matic 4L80E transmission. RPO MT1
-A 2000 GM Packard Electrical/ Delphi Electronics Power-Train Control Module model P01.

By today's standards and newest technology for the power-train...
You have a relatively simple Engine and Transmission Control system.
Almost no electronics in the transmission (mostly electrical components and a basic wiring harness).
Very simple engine monitoring and control via a basic wiring harness and the P01 PCM.

Things should get figured out relatively easily.
Report here any new information as it is given to you; and we will aid you as much as we can.

Keep workin' at it, and good luck!