This 93 XJ6 has 105,000 + miles. It has been running very well. Now there is no power. It starts well, idles well, but will not develop enough power to attain speeds above 30 miles an hour. It does not run rough. When I push on the accelerator pedal, the power goes flat. I have changed the fuel filter with no change.
I checked the fuel supply by disconnecting the fuel line from the fuel manifold, bypassed the fuel pump relay to keep the fuel pump running (if it would. The pump ran and pumped fuel. I live on the Big Island of Hawaii and can not find a mechanic to check the fuel pressure to determine if the fuel pump will deliver fuel at specified pressure. I do not want to pull the fuel tank and replace the pump if it is viable.
Does anyone have information as to how to check the fuel pressure and where I can purchase a fuel pump at a reasonable price?

Present Jag 93 XJ6, Past 57 XK140MC drop head, 59 3.4 Saloon, 63 XKE Coupe, 88 XJ6