Something you may have forgotten to check is the spark plugs, spark plug wires, the distributor cap and rotor and the coil. As stupid as this sounds, 1 spark plug lead that is *slightly* faulty will cause a miss every 30 seconds or so, at "high" power, which is about 2500rpm+, i know, because my car does the same, spark plugs lead no.3 has about 4 x the resistance it should.... OH! One other thing, go to Volvo and get a set of GENUINE spark plugs leads, because they are THE ONLY ONES that fit proplerly, all these generic "REPCO" ones, etc, don't have small enough connectors, while it seems they fit, they don't, trust me on that one! Bougicord are the only ones in Australia that i know of, go to "euro car parts" (they are at revesby in sydney and deliver all over australia) for the distributor and rotor, it's cheap enough to replace even if "it isn't that old"..........Next would be the hall sensor...... Computers usually don't 'cause stupid stalling problems.....
Have you checked AND resoldered the fuel pump relay?
Az