So I've put a few miles on this '88 and it will rev fine in N past 4K without much fuss. On the highway at 60+ if I give it more gas to speed up or take on a hill, it will bog down to maybe 2K and I have to almost completely let off to regain any kind of power. Sometimes it will surge instead and if it weren't for the bogging would probably have plenty of umph to conquer highway speeds. Where should I start?

'87 Raider w/rebuilt 2.6
Weber 32/36