I recently completed my 5 speed swap and for the most part everything went smoothly. On a recently trip I was using Waze and noticed the GPS verified MPH was off from what the gauge was reading. At 65mph, I was actually going 58-59mph. Was I supposed to also swap over any from the 4 spd to account for this? Something else I've done recently was install new tires 27x8.5 r14 on all 4 wheels. I don't recall the OEM tire size but maybe it's possible the tires are slightly different in size and is now causing the difference in actual speed?
That's not too bad most speedos read a bit fast, if you are worried about it, you can adjust the needle. Pull the speedo out of the cluster, move the needle with your finger to 65. Hold the drum at the back of the speedo in that position. remove the needle, they pull off, do not let the drum move. put the need back on pointing to 58-59. done!
I would use the stock speedo gear, but it probably is the tire size change Goggle speedo repair in your area they calibrate the unit