The pumps were never a "problem", and rarely fail on their own. The later pump inserts (the "vanes" part) are only higher volume. You cannot "test" the pump independently, as they are integrated. They work, or they don't, with not much of anything in between. The 1990 700R4 was as good as they got, from production. The only place to go is into aftermarket hard parts, and the Trans-Go shift kit. The shift kit can be installed easily (valve body removal), but the hard parts require disassembly. If the tranny is otherwise healthy, I'd suggest only the shift kit, for now. Once installed and properly adjusted, you'll know what more may be needed. Unfortunately, that's the only way to know, short of complete disassembly.