I used PB Blaster, and *time*.
Soak the base of the distributor, let it sit, give it a few whacks with a brass drift (or similar) down at the base, see if it will budge.
If not, more PB, try tomorrow, or that night.
Took my a couple of days this way to get mine free going at it morning and night like that.

Even then it was too worn to use but at least I had a 'good' core to trade in on a rebuilt dizzy.

No it's not "the same as replacing the timing set".
The chain has no tensioner. When it stretches both cam and ignition timing get sloppy.
I know the computer is taking care of advance on your truck but pull the spout, hook up your timing light, then start and rev the engine.
Watch the timing marks.
Can you see them jump around when you apply and release the throttle? This is from the loose chain flailing around in the timing case.

As I alluded to above, check the distributor shaft for sloppy bushings once you get it out.
IMO, any visual movement side to side is cause for replacement.

Also: Check the balancer for wear at the front mainseal. If there's a groove, you should sleeve it now. Don't forget to oil the new seal on re-assembly.

I hope this helps.