Stuck in Gypsum, CO! HELP!

[matts86chev]

So I'm in the middle of moving from Minnesota back to California. I have my 86 C10 with a 305 loaded down with a Haley Davidson, my toolboxes and some clothes and now my truck won't run right. I drove 13 hours last night and it ran perfectly at 80-85 mph. Then came the Rockies. It was charging up the gradeswell enough at first and then suddenly I felt it lose power and sputter. I pulled over to check oil level, coolant, etc... And all were fine so I tried again and made it to the downslope and coasted down. Then came Gail pass. I had to baby it all the way up right lane flashers on 30 mph sputtering all the way. Finally hit the top and coasted down. It started running great again so I figured maybe it was the altitude... Now here I am in gypsum/eagle, CO. One mechanic told me they had no clue and te guy that works on older vehicles is out of town. The only other option is Midas. I have no clue what's up. I replaced the fuel filter and ran seafoam (before I replace the filter). It seems to e getting worse. Before it would run a bit then sputter then run again now it runs sputters an dies really quick if I give it any gas. It's carbureted too, not TBI. I replaced the fuel pump, fuel line and fuel pump pushrod last summer, replaced the dizzy cap, rotor, etc... Last year as well. No clue. Any help would be great. I'm stumped sitting here with it idling to charge my phone before I camp in the parking lot.
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