[dolluper]

AS you were saying it stumbles at 1500 rpm well thats when about the EGR kicks in check your vac lines and maybe get a new aspesto's gasket and clean it out with a soft face [hate to say it] hammer and knock the carbon build up out of it make sure it at least moves[the vavle underneath ] at 1200 -1600 RPM If the valve moves and you have the same problem I would suspect the fuel pump But you also say you replaced the module did you apply dielectic grease underneath the mod before you installed if not the heat build up could cook it again or give you problems when hotter running conditions
edit: you should have a solinod valve for the EGR on the right side top of valve cover when standing looking at engine front cover[left valve cover] check it for shorts bare wires or not working I didn't think an 83 had one