Welcome to the forum!
1500 bucks is a good deal.
But, a word of caution. A 91 has a 700r4 transmission. The cable from the throttle body to the trans isnt a "detent cable"
Its a "Throttle valve cable"
usually known as a "TV" cable.
And it must be set up correctly.
Do not just start randomly adjusting that cable. You need to follow the factory procedure.
If you dont, you will smoke that transmission.
Sometimes within a block or two.
Dont **** around with half assing a 700r4. it will bite you.
It is an easy to do adjustment once you know how to do it and have inspected the cable and the linkage and brackets.
I dont think your performance problems are related to the transmission.
It sounds like and from the pics it looks like 42 monkeys have been at this truck with random bullshit advice.
The first thing I noticed was those plugs look like somebody gapped them with a forklift. They are not good.
And never trust a "pre gapped" plug
They are pre gapped if the guy in China did each and every one correctly.
They dont.
You need to start with 3 things.
Inspect each and every vacuum line on the throttle body and make sure that they are connected to the proper port.
I would just replace them all.
Next, you need to set your base timing back to zero degrees at top dead center.
First, you need the #1 piston at top dead center on the compression stroke.
Then, take a look at the timing mark on the balancer to see if it shows TDC.
On the passenger side of the firewall is a plastic cover.
Under that cover are several wires.
One of those is a tan wire with a black stripe.
That is the distributor reference wire
You need to unplug that wire before you set base timing.
I will bet you a case of beer of your choice that it is not at TDC and has been screwed with by knuckleheads in an attempt to "make er run"
Fix the vacuum leaks, make sure distributor is in correctly.
Set it to tdc .
And dont **** around with the tv cable untill you know how to do it.
I know, this sounds like a lot of overwhelming bullshit.
But it really isnt.
Its actually a pretty damn simple system.
Dont let anyone convince you that you need to spend more on equipment than you paid for the truck.
Bullshit.
If you can understand how to figure out online gaming, if you ever get called up by us olds farts because we beat the computer with a hammer and it still wont work?
If you get how you can scan **** with your phone and random people drop **** on your porch?
If you get that ****
Tell me.
I have no friggen clue.
The moral of the story is dont let any of the "gatekeepers" try to beat you down.
You can do this. Its easy but its old.
Ill help out in any way I can.
Ill even trade you.
If I help you get it to run,
You explain to me what in the flying **** a voip link is and why I need it and how its worth my time to get one of those damn things and do I need to go to walmart to get what ever that is.
You got this brother.
Its old, but its easy.