I have a 87 K 10 with a 350 (history unknown, but clean inside) it wears a Edelbrock EPS intake, topped with a Holley Truck Avenger 670 cfm carb. It is backed by a TCI truckmaster trans and NP208, along with whatever stock gears are in the 10 bolts. It also has 33" Goodyear MTR's. The issue is, that whenever I get out on the freeway and accelerate into overdrive, it starts to bog or something. It's not really a bog per se, more like the truck can't pull the overdrive gear. I can hold my foot the floor and it will slow down. If I let my foot off, there's a certain "sweet spot" that will let me accelerate somewhat. But without doing that it's done accelerating at around 60 mph. Which really sucks because that's right around the 3-4 shift point, so I spend alot of time hunting up and down through the gears, and use way more fuel than I need to. I'm really stumped, I suppose it could be fuel related, it still has the stock electric fuel pumps in the tanks, except it pulls fine through the rpm range when not in overdrive. I have a new MSD distributor, wires, and a fresh set of plugs to put on it also, but I'm not entirely sure it's spark related either, unless my vacuum advance isn't working properly?