I got a 99 D1 that has been starting to hesitate at interstate speeds (65-80mph). It feels like a plug wire has come off. Sometimes if I let off the gas and get back on it the hesitation will go away, sometimes not. Seems like the problem is getting worse. I have never noticed this at lower, rural driving speeds.

Plugs and wires are fairly new (4k)
Fuel filter has about 8k on it
No check ingine light comes on (it does work)
Air filter is new
use 93 Octane all the time
Blah, blah, blah........

Does this sound like a fuel pump maybe?

Vehicle Speed Sensor

Flame me, but where is the speed sensor?

I just had the same problem with my 96 D1. For me the culprit was the vehicle speed sensor. I believe it is on the left side of the of the transfer box.

A ball end Allen wrench will save you time and swearing.
http://www.kwrtools.com/tballen56340.JPG

I use a piece of hex stock and a socket. It can be something of a pain if you don't have the correct tools.

Also, make damned sure you get the square pin in the hole correctly, otherwise it will tear the sensor apart.

The VSS is on the transfer case adjacent to the parking brake, accessible from the drivers side of the vehicle. To my knowledge, there is no acceptable substitute for the Rover part, trust me, I've searched.

I have almost 200K on the one in my truck, but have seen them fail in as little as 40K.

VSS did not fix the problem. Any other suggestions?

VSS did not fix the problem. Any other suggestions?

I had the same problem when I changed out my plugs and wires and did not tighten the left rear plug enough. It happened after about 4k.

I bought a torque wrench after that. That click sound makes life so much better.

Good luck.

FWIW,
Even though they are almost brand new, it turned out to be the wires. I had two wires jumping sparks to the valve cover at about 3K RPM's.

As much as I hate to say it, this is yet another reason to use a diagnostic tool as most of them would have pointed you right to this problem. Sometimes relying on the gut feeling isn't right. Sorry I pointed you in the wrong direction.

Glad you got it fixed

No problem, I think the VSS was about to go anyway. The square pin did not turn as freely as the new one did. Felt like it had sand it, so I'm sure the bushing it rides on was about gone.