Drag the two computers closer together and see if they can manage 1Gbps when using just a short patch cable.
You have double checked that the actual network cards can both do 1Gbps, and that this is enabled.
If a short pre-made cable works, then time to look at the cable you made, and what exact wiring plan you used. Also to use keystones you have to untwist the pairs, keeping those to a minimum of untwisting is important.