Just off the top of my head...
What kind of road speed are you getting here? If you're getting measurable boost, but the car doesn't seem to be doing anything with it, I'm wondering whether your real problem is a clogged exhaust.
7-8 psi of boost should be giving you scare-the-girlfriend acceleration, and when it does upshift, it shouldn't just fall back to 3. You also mention sputtering and popping: I'm thinking the engine is smothering on its own exhaust.
When was the last time your convertor was touched? Your symptoms fit how my '93 behaved when its convertor got corked up.
-- Andy Green