7' X 4' Combi

[Jonathan]

I wrote a quick bit of G-Code (my first bit of G-Code writing.. (Thanks for the tuition i2i)) just to watch the gantry going back and forth and stopping and starting with small travel and big travel just to see if everthing is how it should be, then copied and pasted it several times, then just watched it run for 45 min

Try this spreadsheet to generate similar G-Code. Especially if you just test one axis, the machine can seem fine from just jogging around at full speed, or repeated code like you tried, but in reality fail a test with random code. The reason is if you just repeat the same commands and run it for a long time, that's not much better than just running those lines a few times since it's doing the same thing every time, so the currents will be virtually the same every time. If they're randomized then over time you can expect to find if there's a problem.

Edit: also what acceleration have you set it to?