5.2 magnum options

Sounds like intake is not problem, nor broken valve springs as they make vac gauge jump around. You need a known good carb and ignition. Even if you swap dist out for points, its easy to bypass the MSD. If you are running factory oragne box, swap it for know good, very common failure. Newer msd go bad often too. If you remove all unknown variables then the problem will present itself to you easily. Got a buddy with some parts you know are good, try them out. Sounds like you wont even have to drive it to figure out if its fixed so dont bother with throttle linkage or kick down, bolt it on and start it up. Take you timing light and check for constant spark on each wire, if not swap out box.