Stumbling on ONE hill.

Hi guys, hope everyone's having a great holiday season and enjoying their time off if they got it!
So right before Christmas I was returning from a clients property , taking my normal route home, and everythings working like normal. I hit a brutal hill that I always have to gun it then downshift to hope I can make it up going the speed limit ( woohoo 120 horse!). So halfway up the hill, about 500rpms from my downshift point, the car started bucking and stumbling incredibly rough, firing only two possibly even only one cylinder. Downshifted to try and recuperate some power and it was worse, so I put on my blinkers and limp up the hill in first, stopped at a gas station and shut her off. Checked all the spark wires and connections, checked coil connections, everything is fine. Start her right up and everything was fine, no stumbling AT ALL. Drove home and drove for the past 4 days no probs. so last night that client calls and I run over there, and on my way up the SAME hill, only coming up the other side, the same thing happens!
Stumble back to the gas station in 1st, only didn't shut her off this time. Idle did not appear to be errattic, checked all connections again, no apparent change. Got back in and drove the rest of the way, did my work and drove home with no problem.
Purchased new cap, rotor, a super stock coil, 8 mil wires and plugs. Is there anything else it could possibly be? Could it have anything to do with the fact I removed the old carter carb and replaced with a fully mechanical weber?

1984 Wagoneer (XJ)
2.5l with weber 32/36, no emissions equip.
Ax5
Np207

I think doing the tune up stuff is a good idea.

If the tuneup doesn't fix the issue, I'd check the float level and movement in your new carb.

Stripped of emissions stuff, different carb, and it sounds like the ignition system is no longer stock. Where to start?

'500 rpms from my shift point" --- exactly how many rpms is that?
"Brutal hill" --- how many degrees?

So this is your "Normal route" home? After which mod did the problems start?

Are you still running the GM distributor, ignition module, and resistor with your low impedance coil? What coil is it? Perhaps the ignition module is overheating which is not uncommon when you switch to a "hot" coil and would cause intermittent ignition. This would not clear until module cooled.

Why did you swap in the new carb?
Did you set the floats? (loading would clear after you cleared the hill).
Is the carb sized properly to the application?
Did you upgrade or replace the fuel pump?

So many variables.

This is on a stock ignition system. Stock coil, modules etc etc. I've had the new carb for over a month and it's never happened. I have yet to receive/install any of the tune up parts. The hill is my normal route home and it's never happened before the last 5 days (however it has been pretty cold). I normally downshift at 12-1500 and up at 35ish
The stumbling really appeared to be occurring under load.

Are you using carb pre-heat, or did you get rid of that with the cab change?
Carb icing is a problem under certain conditions if you don't pre-heat the air coming into the carb.
The symptom is dropping of power underload, and acting as if the choke is on when warm. The harder you push on the gas, the worse it gets.
Eventually is will stall out and after a bit of sitting, will restart.
Easily identified. When it's acting up, lift off air intake to carb and look for a snowball in the carb throat.

Other than that, I would hit the ignition system.
I had a cap and rotor crap out on me and it would only act up under load. Might start there. If the '84 2.5 uses the same GM Ignition module that the 2.8L did (Mounted inside the distributor), I'd replace that - just because.

There is no carb pre heat. How could icing be seen or identified?
This happened again 3 times yesterday, all 3 times on the highway.
Twice in 5th, once in 4th, at around 3-3200rpmstarts out as an audible 'vibration' noise, then the car coughs, misfires and it gets progressively worse, no matter what load, unless in neutral where it revvd smooth as butter. Fix was the same, pull over, idle sounded 100% normal, jiggled all the wires, no difference in sound or operation, hopped in and took off. No problems till it started again.

sounds like classic spark pug wire/s failure to me

That's what I figured I was just making sure it wasnt something more serious. Thank you for the replies!

This sounds like spark failure to me, but one other thing occurs as a possibility, depending on the hill and the carburetor. Is this hill just a little steeper than every other one you drive up? If so, it occurs to me that the slope may be just enough to make float level in the carb an issue.

Sounds like beginning signs of Fuel pump failure to me..

I had a fuel pump that hated 1 hill.. Never showed signs of failure anywhere else but the whole car would bog on that hill and I would question if I was gonna make it.. Pump died a few weeks later, once replaced.. everything was back to normal