Suspect your speedometer may not be reading accurately?
There are three different types of speedometers that are matched to the tyre size of the Land Rover – The standard tyre size on a Land Rover 109 was 750×16 and the standard tyre size on an 88 was 600×16, therefore the speedo would need to be calibrated differently for the tyre size on the vehicle. A 109 should have the code 1408 on the face (1408 turns per mile) and an 88 speedo with 600×16 tyres should have the code 1536 (1536 turns per mile).
Therefore if you have an 88 that has 750×16 or metric equivalent tyres with the original speedometer, it is likely to be reading inaccurately. The following info shows which speedo code matches which tyre:
1408 7.50×16 (235/85 r16)
1504 6.50×16 (205/80 r16)
1536 6.00×16 (205/70 r16)