My 93 Honda has been acting up when I reach speeds of 70 mph. It lurches and falls back with the tachometer jumping around. It feels like it can’t get gas, but my mechanic can’t find anything wrong and says it can’t be the fuel pump or fuel line, as it would happen in city driving. Help.
I think it could be the fuel pump, but I would not bet on it. Of course you could just drive the speed limit. 
Your mechanic could be wrong. Here’s what you need to do. Find a relatively unused stretch of roadway and do a full throttle acceleration. If you start to feel power losses and inability to reach high rpm’s in the lower gears, then it could be the fuel filter or fuel pump. It could also be the shaft bearing in the distributor, or a number of other things.
Your tachometer gets its signal from the ignition control module in the distributor, doesn’t it? With the tachometer erratic, I think the ignition control module is getting over-stressed. To keep the stresses to a minimum on the ignition control module and the ignition coil, the spark producing parts should be fresh…fresh spark plugs and wires, distributor cap and rotor, are a start. Of, course, the air filter and fuel filter should be recent, also.
70 MPH if not 75MPH is the speed limit in some rural highways
I had the dristributor replaced when my car was losing power and had to be towed. He initially worked on the the spark plugs and after the 3rd time in the shop he finally replaced the distributor. It no longer lost power and died in city driving, but the interstate speeds are presenting a continuing problem.
A shop should have an engine analyzer to test the firing voltage on each spark plug wire. It could show the firing efficiency and voltage, in kv (kilo-volts).
The spark plugs, and spark plug wires, should be recent, with the ignition problems the engine has been having. The connections of the spark plug wires to the plugs and to the distributor should be doubly checked. I wish the design made more positive connections; but, it doesn’t.
Just change the fuel filter. It’s no big deal.
The fuel pressure is best checked (after the fuel filter has been changed) with the automatic transmission in DRIVE, and the engine pulling about 1500 rpm for 3 to 5 minuets. This puts a more “real world” load on the fuel pump. If the fuel pressure falls off, it shows that the fuel pump couldn’t keep up at highway speeds, either.
It’s 75 mph in most of CO and NE, driving less than 80 will make you a roadblock.
A car can’t perform if it is short of gas, air, or both. First make sure your air filter is clean and not partly plugged. Next would be a plugged fuel filter. All the other advice makes sense.
You could do a fuel volume check to see if the pump is putting out the volume it needs to. What I have done is hook up the fuel pressure tester and tape the guage to the windshield. Then see what the pressure is when you get up to speed.