Searching for cause of variation in speed

[gwtw]

Hello, with my HZJ75 when in fourth gear and driving 45-50 km/hr I am experiencing some speed variations / hick ups. Not really bad yet, but I want to prevent worse. I have done following:

1. Dieselpump revision 25 k km ago
2. Diesel filter change
3. New glow plugs
4. Test driving with a Bosch Diesel Service specialist: Not caused by diesel pump or injectors
5. On car inspection of rear propeller shaft. No play or obvious wear in the spider bearings. I can rotate the propeller shaft by about 10 mm (3/8 inch) when I measure it on the flange of the rear differential carrier.


Where do you guys think I should start looking?

 

[Squash]

Try not to drive into a head wind!
Think like a sailor!
Drove my 1985 bj70 from Sudbury Ontario to Alaska, Yukon and the NWT.
Wind wind wind.
I took every advantage I could, exploring by day and hammering out the miles once the air calmed down.
Best thing is a wicked tail wind, brings on incredible horsepower and fuel economy!!!!!

 

[roscoFJ73]

Where do you guys think I should start looking?

When did it start happening? It could be air getting into the fuel lines or maybe a blocked fuel pick up in the tank. Or does it feel like the drive train?

 

[Squash]

As Rosco stated fueling might be the issue but you mentioned only in fourth gear.
Your speed seems low for 4th gear because she's such a dog of a gear.
Guessing you have a 5speed?