Transmission shifts only at high revs.

[SVXR92 LSL]

What would be the cause of this? Would repair be feasible or replacement of transmission be needed? The reason I ask is that there is a 92 pearlie for sale for very short money near me. I'm new to this vehicle (SVX) and any help would be appreciated! Thank you in advance....Still learning and feel like a bit of a.. !!

[SoCal LS-L]

I think ive heard of low internal fluid pressure doing this..... have you replaced the fluid filter inside before? Im sure more ideas will be along shortly, there is also a mod having to do with the TPS that causes the trans to shift at higher RPMs as well..... possible this was done with the car prior or there is a problem with the TPS?