What I don't get in this 4+yrs old post is this: the service bulletin tells us to use some Williams parts (cap, EOS switch) on the Bally linear flipper mechanism and these are the upper mechs in Truck Stop. Aiming at I and T in C-I-T-Y and not C and Y.
How this is going to solve a weak lower flipper problem (Williams mechanisms with strong FL-11629 coils) is incomprehensible to me.

Years later… my Truck Stop plays with standard pinballs, and trying smaller ones results in ball trough malfunctions.
I‘m guessing there are two versions out if someone‘s really using those 1inch balls.
Thought I should add this info nugget even if the thread is somewhat old.