Purchased a 89 Range rover, having issues with it. Help

Long time toyota guy and I just purchased a 1989 Range rover for next to nothing. Problem with it, is I cannot get it to go above 30 mph. In the shop at a idle it runs fine, but on the road it has no power.

Did the usuall, cap, plugs, rotor, fuel filter, ect. Checked the wheels for binding ect, all are free.

The EFI light is on and I tried to ohm out the throttle potentiometer, like the manual says, but it does not seem adjustable like the book says. Also with the timing, I have read the book front to back, but I am clueless on how to set it. On the pully by the crank, all I see is 1 big mark on it. When I try and set the distibuter to that mark, with the vaccum off, it runs real crappy. If I turn the distributor, so the vaccum can is close to the thermostat, it seems to run the best. It says to set it too 6 degrees, but I cannot see any marks anywhere that say 6.

Any ideas or any know issues that they have. The rig has 100000 miles and appeared to be somewhat taken care of most of its life.

Thanks

What is the fuel pressure ? No nipple to check, need to tie into the fuel filter lines, pain in the ars. Start with the basics.