It seems to me like you may have either a kinked hose somewhere near the in-tank fuel pump opening, a blocked or kinked line leading to the carbon canister, a blocked rollover valve or possibly a problem with the tank balancing plumbing.
I haven't encountered this problem on my 965 (or heard of it on any).
The tank on 900 IRS cars is quite different to the live axle 700s and 900s as the pics from the parts book (below) shows.
See Drawing 68956 from the parts book below (components list is found in Group 23, page 277 of the 900 94+ parts manual, which is PDF page 269 of the downloadable version from GCP).
As can be seen above, the are two halves to the tank; there's a section where the tailshaft runs through the middle of it and the tank is protected by the shield [14].
Pipe [10] above forms part of the tank's balancing system.
The tank balancing system is shown here, in Drawing 68950, below.
Note - they changed several items and the tank itself a couple of times, then revised more items in YM 97-98.
The drawing above shows the 2 variations - the top one, with funnel [15] doesn't have a carbon canister system; the hose [13] in the lower drawing actually goes back from the rollover valve [8] to the carbon canister, which is shown on another page (Group 23, page 261 to be precise) instead of just sitting there doing nothing like a Camry in the overtaking lane.