What you need to do is rule things out.
Lift the tank check to ensure the fuel pipe is not kinked and routed properly, it should be routed under the frame cross brace and not over it.
If it is over it reroute it under the cross brace
Check the flow from the Fuel tap, lift the tank turn off the fuel tap pull off the hose and attach a long piece of hose to it. direct it into a can, turn on the tap, there should be a full even flow.
Next is do what Joebloggs suggested, rule out a blocked tank vent and ride it with the fuel cap open. If it is ok with the cap open, clear out the tank vent. Press in the two clasps to release the key and put the cap down but not closed.
If the problem still exists, bypass the pump by connecting the pump outlet to the fuel filter outlet, now fill the tank to the absolute brim, a full tank will not require the fuel pump. If it is ok now replace the pump.
Let us know how you get on