You changed the breaklight switch and fixed it. WAG Oh I see your is manual now so my next thought is your clutch is slipping causing a shudder when its hot and the clearance open.

 

I DONT WANT TO KNOW.

 

1st wag was a time and distance.
2nd would be related to temp.
Iam still at fuel. Possible air.

Bill

 

Hows about the thermostat was sticking and in stop and go driving the engine was warm enough to run well but at prolonged periods of high speed driving the engine would cool too much resulting in poor driveablity at low rpms/speeds until the engine was back up to temp. SWAG!

 

did your injector o-rings fail? then clog the screen inside the fuel bowl?

 

Doubt it's fuel related. Restricted fuel supply should have an impact at higher rpms also.

Since these motors don't really get to operating temp around town and the syptoms dissapear after some time...My guess is that its temp related.

 

The under hood light bulb burnt out!

 

you ran out of plutonium for the flux capasitor? or because of the speed limiter you could not hit 88 mph?

 

or your trailer brake controler

 

The spark plugs are worn out.

 

Lmao y'all are jerks with the past 4 post have my laughing in the middle of class and everyones looking at me haha, good stuff. my hood bulb dont work

 

Try cleaning the windshield...worked for me!

 

Summer air in the tires?...

 

wow I missed all the fun while I was working on a cheby,
so I don't have to reply to every post I guess I will just tell what I found and how.
last week my shop was slow so I decided to pull the injectors and install the new o rings (I bought them 2 or 3 years ago thinking it was the problem) but never installed them as I have never add oil between oil changes and have never had fuel dilution.
So I pull the driver side valve cover, pull all the injectors, put new o rings on, installed new injector harness due to 1 glow plug wire being bad since I have owned the truck.
new valve cover gasket, new end on front wire harness (glow plug pin burnt)
I than have to run my daughter around so I button it up and go. runs fine, trip to the diesel drags in Phoenix runs fine.
decide to cut the 3 good glow plug wires off of the harnesses (repair ends for the 7.3 IDI) when I busted the plastic apart on the front harness the ground wire was broken in half just before the split where it goes to both injectors.
when the engine was cold or just warm it would make good enough connection to fire the injectors, after a long trip the wire would move enough to lose connection causing the miss, once it cooled down a few degrees it would make enough connection to run right.

this made it almost impossible to trouble shoot because to get to my shop there is a 1/2 mile stretch of 45 mph, a stop, 3/4 mile 45 mph, 1 mile 25 mph than 1/2 mile 25 mph.
so by the time I would get to the shop it would be running fine.

found it by total luck (and being too cheap to buy repair ends for the idi glow plugs).

 

lucky find.
and no winner among the bunch of us....