100 kph= 62 mph
130 kph= 80 mph
I rebuilt my mono on my 250 and basically set it up to spec. No trouble cruising at 70 mph. Your gearing may be different so a tach would help in determining how hard the engine is working.
You may also want to check your pump fuel flow output and check for any restrictions like clogged fuel filters or bad fuel hoses. Pump output should be around 4.5 to 6 psi and pump at least 1 pint in 30 seconds or less.
Here's a good site. It's for 75 to 80 something trucks but should be similar.
http://www.73-87.com/7387garage/drivetrain/fuelpump.htm