As I recall, a disconnected oil pressure gauge (ie sender open) on these later cars will peg the gauge to the max. So you could have left the wire off or interrupted the connection somehow. I would suspect something physical related to removing the instrument panel, for the oil gauge.
You really need the TSM to test the fuel gauge, in order to know the resistance range of the fuel sender. The sender is very easy to test. Did you test the sender with your multimeter for ohms at min and max before replacing? I suspect not. If the old sender tests ok (ie gives the correct ohms readings at min and max), you can use it as a tester for your gauge. At the gas tank, connect the sender wire to the old sender and ground the base, and move it over its whole range. If the gauge does not move, that indicates the gauge is not functioning.
It's possible that you have a bad connection between the sender and the dash. Remove and reseat any connectors between the sender and the instrument panel. Hook up your old gauge at the tank, and measure the resistance from the gauge wires (disconnected from the gauge) to the sender. You should get the same readings through the sender wire and ground that you got by testing the sender directly.
If the wiring checks out, and the sender tests right, then that leaves the power source or the gauge. Did you test power to the gauge? I don't know whether it should be 12V or some regulated voltege - the TSM will tell you that. But if the wires are ok, you have power to the gauge, and the sender works, the gauge has to be kaput.
1) '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps. 2) '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR 3) '75 CJ-6, 304/T15, PS, BFG KM2s, soft top 4) '95 VW Golf Sport 2000cc 2D