I think you have two problems but let others chime in as well. At 2k rpm i believe you should be seeing more advance from the mechanical advance. Base timing should be 7 degrees, at least on my 89. I believe your mechanical advance may be sticking. 30 seems a bit high for the vacuum advance, especially if your mechanical isn't engaging. When I replaced my distributor this summer, it was listed as working with a ram 50 or starion. The vacuum advance unit that came on the distributor was pulling way too much advance causing all kinds of pinging under light cruise. I had a new vacuum advance unit and I swapped it out and it was fine after that. There were numbers stamped on the arm of the vacuum advance unit. The distributor I believe came with a "12" and the new one I had on the shelf I believe was stamped "10". I'm guessing it's mm of pull, but I'm not sure. Someone on here who knows mitsubishis better than myself may have better technical information than that.
I would start by disassembling the distributor. Mark the gear with witness marks before pulling it off the shaft so that it goes back on the same way.
Check the mechanical advance linkage for any binding or scoring. Also, see if there are any numbers stamped on your vacuum unit. I'll see if I can dig mine out in the garage to confirm the numbers.