intermitent perfomance, high reading on tacho & temp

[Bracky]

hi all, still having problems after the conversion. The power comes in intermittently + the rev counter and temp gauge in the cluster are reading too high. The taco reads off the clock at around 2500rpm (guess) and temp starts at 3/4 and goes up as it warms up.
So far i have added a second earth strap to the block and used 0 gauge wire for the rear battery conversion, from the front distribution point the fuse box is 4 gauge, the main ecu/dde relays are running on 8 gauge and a pair of 4 gauge to the starter/alternator (will be changed for a larger single cable soon)
I've started going in circles in my head now and could do with some much needed advice.
Thanks in advance