I have a 1983 F250 XL 7.5L 460 engine. The speedometer seems to be off. The meter seems to be higher then actual speed. Is there a way to calibrate? I've also noticed my fuel gauge doesn't always read. I'll switch it to rear tank and it will go on E since no fuel but when I switch back to front it won't change. Sometimes it will change back but not every time. I thought I read that maybe a bad voltage regulator on the circuit board in dash could cause these issues. Any ideas?