I have mined Gapcoin with GPU's in the past.

Realize that the current GPU miner has not been tested and/or upgraded for newer GPU's and the prime sieve still utilizes CPU.

GPU mining has not yet been necessitated through competition against the network difficulty. Most users are still mining with CPU's.

As the network difficulty increases, Gapcoin will fine new Prime Gaps of highest merit.

New development of GPU mining software and pooled mining will also enable Prime Gaps to be found in higher shifts.

Gapcoin has never reached a higher network difficulty of 50. When we do, perhaps more people in crypto and mathematics will pay attention!