Oil pump drive gear

So my question is this...How often should the oil pump drive gear be replaced?
I have just built my 318 and other than the distributor and the oil pump gear, everything is new...
I am experiencing a miss situation when I keep the car at a constant speed or take my foot off the gas...POP-PA-POP.
The car accelerates fine, but when just cruising it does this.
I am working on getting a new distributor, I just wondered if the drive gear could be bad..The old motor did the same thing before I took it out.
If I need to change the gear..will I have to take off the intake to do it?
I imagine there might be a special tool to grab hold of the gear through the distributor hole.
The motor details are:
318 bored .040 over.
KB Pistons
273 forged crank
"302" heads
comp 268 cam..pretty sure on the number...maybe 286.
edelbrock performer manifold
edelbrock 600cfm 4bbl
Electronic ignition
factory manifolds dual flowmaster
4 speed trans
65 Barracuda
Sorry this is so wordy...sometimes I just can't stop myself !!

Any ideas on the gear replacement or miss situation would be great!
Dan