383/496 stroker bogging on highway

The vacuum seems low for a 496 with a hydraulic roller and that static compression. What are the cam specs?
It may be a volume-note-due-to-the-pump issue. The owner of the 496 I did has a much larger carb and automatic, it makes about 580hp, and it's being fed by a stock appearing Carter mechanical pump but using a 3/8 line and sender.
Some things to look at: from tank sender to carb needs to be 3/8" diameter (or -10); the MP ignition has the right centrifugal curve and that the module is grounded well; and if it's an orange module I'd toss it in favor of a Standard Ignition LX-101or the MP chrome box.
Lastly - you really need a larger carb. There is a problem with "too small" of a carb and that is they get very hard to tune well because you're using it outside the expected performance window of the manufacturer. It's not that it won't work, but it needs a lot of adjustment that may or may not be easily done (air bleeds, etc). So I'd suggest you get a carb on there that will work better. That 496 I mentioned gained about 25hp with a larger carb on the chassis dyno, and gets 13mpg on the highway.