98 5.9l Ram.
My dad told me that he's getting a hesitation while cruising.
It does it while in gear (2nd, 3rd. and overdrive), not while shifting.
The tachometer doesn't budge when it hesitates.
It doesn't do it every time he drives.

I tested the TPS and it seems right by the multimeter.
I tested the vacuum and it seems right to me.
The transmission fluid smells/looks right and is at the right level.

When I was talking to him about it I was describing how it should feel like something grabs the driveshaft to slow it down a little when the transmission shifts because of how the kickdown bands work and he said that's exactly what it feels like but not while shifting.
I am going to get the diagnostics ran at my local transmission shop to see if the governor pressure sensor is reading what it should, I'm thinking changing that might be the next course of action.

I'm stumped.

Here's a video of the vacuum test. I have the tester connected to the nipple under the brake booster hose.
http://www.youtube.com/watch?v=GDhGUj3s5LE

Here's a video of how to check the check valve on the side of the intake manifold. I thought the readings were off until I realized that I was connected after a check valve. I have the tester connected to the T that goes to the cruise control servo.
http://www.youtube.com/watch?v=X3HQKhVzzUk

 

I'd take a chance and replace the TPS. Or better yet, swap it with the one on your truck.

 

I think I have an old one laying around from when I changed mine thinking my 300 rpm surge was caused by it but it was actually caused by a melted spark plug wire grounding to the block.

 

My dad told me that he felt the hesitation really bad when he floored it one time and hasn't done it since. I punched it from a stop earlier and got to about 4000 rpm (hit 60mph and had to let off) and felt nothing wrong.

I took it to a transmission shop today and from what I see, there's nothing wrong. I was the one looking at the $7000 Snap On scanner while the tech was driving the truck and telling me what the readings should be and when. The scanner told me that the TCC and O/D were working as they should, when they should. Also, the governor pressure was reading what it should when it should.

The transmission has firm shifts, as it should.
The scanner showed that the TPS is working as it should. I also checked the TPS with my multimeter and didn't see any flat spots in it (jumps in the voltage as I turned the throttle).

The techs only guess for the hesitation that my dad is feeling in the middle of his 25 mile highway drive at 65mph is that maybe he got ahold of some bad gas.


Now onto the only issues I found in my 30 mile drive today. It feels like his rear tires need to be balanced (his front tires are new).
I felt that hesitation he talked about once in my drive. I was doing about 30 and floored it then I felt the hesitation and noticed as I watched the tachometer climb that it hit 5500rpm when it did it. Sounds like a rev limiter to me, hmm... What would cause the truck to not shift at 5000 rpm (red line) like mine does and instead bypass that and hit the rev limiter at 5500 rpm?

 

Over the course of the test you lost about 1.5"/Hg, about 0.5"/Hg each time you revved the engine. If the engine was at normal operating temperature when the test began and the tachometer settled back to the same value after each rev, I'd be inclined to suspect a slack timing chain.

I wouldn't expect it to cause a random hesitation, but it might bear looking into some day.

Oops, forgot your closing question: Banging into the rev limiter without shifting I would expect to be the governor pressure solenoid flooding, not a big worry but something to keep in mind so the pedal can be feathered to induce a shift when passing those idiots who creep up to passing lanes then race through them.