I don't think it's a good idea to base ride height on visual, that's going to make it VERY difficult to get a consistent tune.
I suspect you may have a bunch of other issues causing problems aside from your ride height.
Worn out drives and dig in and catch the pins on the shafts causing the diff to lock and truck will spin out. If you haven't rebuild your diffs and the fluid is empty, then you could be diffing out.
Generally it's best practice to do a complete rebuild of the car every 15-20 battery packs in order to ensure you get consistent handling so it drives exactly like it was when it was brand new.
A rebuild consists of pulling every bearing, cleaning and inspecting for any sign of crunch when you spin in your hand. Slight gritty is okay to carefully pry the rubber seals with a hobby knife and flush the bearing with WD40 Dry Lube and repack with fresh grease and snap the rubber seals back in place. Then you want to clean and apply fresh grease on all rubber seals in the diffs and shocks as well as fresh fluids.
Fluids should be a milky grey... if they are brown then you have too much dirt mixed in, black is worse and no fluids at all can be catastrophic to plastic parts and create a chain reaction of over heated/melted plastic.
Make sure there are no flat spots on your pins as well:
Good Luck!