90 DeVille stalls when tank under half full? Wtf?!

90 DeVille,, 4.5 v8. Car ran great till smog time, Svc center got it to pass but basically destroyed my car, it’s never been the same since they had it. Here’s my problem, I stall when coming to a complete stop or slowing down ONLY when they fuel tank is less than half full. When it’s above 9 gallons, it runs great. New distr c&r and ignition coil, ISC motor, tps, alternator, fuel pump , battery good, for tested good, plugs & wires new, starter fairly new works great, stall reproduces in any gear including neutral, sender needs replacement (not a biggie) , only prob I have is gas tank leak! I use permatex which has been working pretty good, I had one pinhole leak, then another after a week, will replace tank when payday comes. I was concerned about the vapor canister, I gotta find out how to test that thing! I think my tank is just so old that the metal is getting weak and the pressure is making it constrict and leak.. I was getting p53 and e26, distributor signal interrupt and shorted tps, Changd both, cleared codes, patched up tank, filled her up, running great, and when fuel gets low I’ll post whatever codes I get. Please help or offer suggestions if this sounds like something you have encountered! Thanks!