1986 BMW 325 won't go uphill

i just bought a 86 325e it ran good despite having sat for eight years. I ran out of gas 2 days ago and now it seems to be running good but then won't go uphill at all. I put fuel injector cleaner in the tank. I changed the fuel filter. Still won't go up a hill at all but otherwise runs great. Do I have to drop the tank and clean the fuel pickup or is it injectors or what help please ?