1980 4x4 20r pickup. Engine rebuilt finished February 2019. No issues for one month.

The problems I've got now.
1. Stalling while coming to a stop or idling. (Resolved (hopefully))
2. Sputtering when decelerating in gear, especially downhill.

The first day I noticed this was a Friday and I didn't have time to look at it over the weekend. I left it at my friend's house. Took it to the shop on Monday and same problems were there. These two periods of driving were 10-15 minutes each and it was pretty consistent with sputtering on deceleration and stalling at stops or idles. Every hill and stop was a chore.

The shop I had it rebuilt at test drove it Tuesday morning and evening and could not duplicate the problems. I picked it up Wednesday morning and sure enough I found it hard to duplicate the issues until I went down a steep hill in second gear.

I drove the pickup for about three hours Thursday and the problems are now very subtle. I bought a fuel system cleaner and added it. There hasn't been any problem with idling or coming to a stop after 90 miles of driving with cleaner added. The sputtering happens infrequently now, but most often occurs in 2nd/3rd gear while decelerating down steeper hills. Occasionally it will sputter on flat deceleration.

I checked all the lines and hoses last night for problems and actually found that the knock sensor was loose and maybe disconnected. Reconnected that but the sputtering is still there this morning.

There is a minute amount of oil in the air filter, but figured it might be from breaking in the new engine.
I've been reading through a bunch of threads so I have a good idea of what I can check for. I'm going to replace the distributor cap and rotor and go from there. My buddy is going to help with testing/replacing vacuum lines and vtv. My repair manual is on the other side of the state right now so it's a lot of googling going on right now.

If anyone has ideas for things I should look into besides what's mentioned that would be great. I don't have time this weekend to go in depth with anything so it's going to be a lot of little things here and there.

Update: 03/15/19 17:29
Distributor cap and rotor were slightly corroded but putting in new ones did not resolve issue. Can't get a VTV this weekend so that will wait. Found an issue with the "IN" line for fuel pump. After shutting engine off there is a very quiet hissing sound and moving that line corresponds to the sound. All 3 lines are older so I'm going to hit up Napa tomorrow for some new ones.