My story goes on. I took the injectors out and ran a bunch of cleaner through them. I hooked the injector solenoid up to a 6 volt flashlight battery and operated it open/closed many times as I sprayed carb cleaner through it. I'm not satisfied I could really clean the tiny orifices but It couldn't hurt. Reinstalled the injectors and took it down the road. No change in the performance. It still stops accelerating at about 65 mph. I have ordered reman injectors. Now I wanted to check for stretch in the timing chain and I think I've found at least part of my problem. I put a 32 mm socket on the damper bolt and turned the crank clockwise until I was sure all the slack was out of the chain. I put a soapstone mark on the damper right next to the 10 degree ATDC mark on the timing chain cover( where you set the timing). Then I popped off the distributor cap off where I could see the rotor button. While my wife watched the rotor button I turned the crank counter clockwise until the rotor just moved then I looked at what timing mark the soapstone mark lined up with. I did this a few time and the average was 12-14 degrees of play in the timing chain. This is too much so now I'm tearing out the timing chain. I should have that done tomorrow. I'll let you know how it turns out

 

Well, I got the new chain in and there was very little improvement in power. I'm going to go back through my analysis/tests and see if I missed something. One thing I will try first is disconnecting the exhaust pipes at the y and running it wide open without the converter/ muffler. Maybe the measurement I took on converter back pressure was bogus.

 

I disconnected the converter and muffler and went down the road. Other than sound cool, there was no improvement in the power, still 65 mph max. I had ordered reman injectors from Rockauto and when they came I installed them and the truck wouldn't start. Both the reman injectors were faulty. I sent them back and ordered new ones. They are on the way and I am driving with the original injectors.

 

It's been a while since I added to this thread and I have done several things but nothing has solved the problem yet. The problem is the truck won't go over about 65 mph on the flat and if I start up a hill it will slow up from the 65. The motor appears to run smoothly just no more power. The things I have tried are:
1, New injectors, MAP, TPS, Temp sensor/sender, O2 sensor, computer
2, Disconnected the exhaust so no back pressure
3, The only codes is has are 12, 34 and 55. 12 means it has been less than 50 starts since the battery was disconnected, 34 is for the speed control solenoid if it had cruise. It doesn't have cruise so this code means nothing. 55 means that there are no more codes to report.
I finally gave up and took it to a shop. They couldn't fix it but they gave me a clue. They weren't transmission people but they thought it might be the OD wasn't engaging. That would have been a help except this transmission doesn't have an OD. And here is the clue, it is a 3 speed A/t with a locking torque converter. If this isn't locking, could it cause the 65 mph max problem I'm having? Somebody out there has had this problem I'm sure. I'm almost three months and much $$$ down the road and I still am stuck. What do you think?

 

I'm trying to remember if you've added a vacuum gauge to the truck. Anymore you get combination vacuum/boost gauges. If it were me, I'd have a dash mounted gauge and watch what it does when the engine falls on its face. As for the lock up feature causing the fault, it shouldn't. All that does is increase fuel efficiency. Is it possible your truck might have a speed limiter? Possibly a company owned it and wanted to limit the speed for the drivers. I've seen that before, but it's usually easy to find.

 

I did check the vacuum idling and it was about 18. I’ll try checking it at speed. What should I look for? I’m the third owner. The first two were from a single family so no governor

 

18 inches of vacuum is a mechanically solid engine. No problem there. You want 17-20 inches and you're right on the money. I worked on a car once that 2 dealers and several shops couldn't track down. An internally rusted piece of the exhaust would blow shut and restrict the exhaust flow. This will show up as a quick drop in the vacuum draw. On the one I worked on, it would drop from 17-18 inches to 5. The car fell flat on its face. Once the bad exhaust part was replaced, it ran like a sewing machine.

The reason I mentioned a dash mounted gauge is it will also let you keep an eye on fuel consumption. The higher the idle draw, the less fuel you're using. On the car I tracked down, we took the hood off and drove around with a large gauge propped up on the engine. It was a '64 Buick and took three people to remove and then replace the hood.

 

Look on your passenger side exhaust manifold, You should have a valve on it. This is used to help warm up the motor when it's cold. Problem is they tend to stick and if it's closed will restrict the exhaust. You should be able to move it by hand.

 

The heat riser valve is free and the spring easily returns the shaft to the closed position when cold as it should. I'm going to get it hot and make sure it stays open.

 

I had read that about the dual wall pipe in your first response a couple months ago and I checked mine to insure it is only a single wall exhaust pipe.