Sounds to me like a linkage problem pulling more toward low range, get underneath and have someone move from high to low and see if there is too much tension pulling high toward neutral.

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Beaten up old 98 Gen 2 Liberty, 13.0, stock V3 STI running gear.
07 Transit motor home
69 VF & 70 VG Valiants needing full restoration
Yamaha Zooma 50cc rocket hopefully going with the Transit.