I wonder if your "Throttle Breakover Spring" is broken.

It consist of some linkage, that is spring-loaded one direction, BUT it allows for some additional movement, when the governor shaft is a MAX throttle, but your OEM throttle linkage is still pushing on the shaft.

 It's purpose, is to relieve, this extra pressure, off of the governor shaft and bushing, allows for some engine and/or cab movement and still achieve full throttle.

Now, if it is broken, then you don't have any solid control , of the engine throttle. The governor throttle shaft  "can" bounce around, inside the "breakover slot" Because the spring is broken. This could give you the complaint of surging.

It is easy to test, get a flashlight, and grab throttle linkage and move it ALL the WAY, to HIGH IDLE (MAX RPMS). Engine can be OFF (non-running) to check this. Here's what you should feel/see = throttle should move with governor shaft(pivot shaft) UNTILL, you get to the MAX RPMs limit, THEN you "should feel " additional spring tension, as you move throttle linkage even farther (causing the breakover spring, to twist; assuming you have a good spring)

Edit: I should warn you, a good spring, inside a throttle breakover Assembly, that isn't bolted on, is a little dangerous.

To assembly; You tend to use a vice, to grab the inside part, then add spring, then lastly you must "twist" the outer part and push the two pieces together = this creates the spring-loaded condition. It "could" fly apart, if you don't get the two halves, pushed together closely enough, during reassembly. It is safe, once you have it bolted back on governor.  

(3208 throttle.jpg)

(3208 fuel pump.jpg)

(3208 pump without throttle linkage.jpg)

(3208 pump side view of throttle breakover assembly.jpg)

3208 throttle.jpg (72KB - 1037 downloads)

3208 fuel pump.jpg (43KB - 1009 downloads)

3208 pump without throttle linkage.jpg (27KB - 1031 downloads)

3208 pump side view of throttle breakover assembly.jpg (57KB - 1003 downloads)