I have a 91 DOHC 5sp that pops out of reverse, and doesn't like shifting into 1st quite often. 2nd can be difficult too, but usually goes with some force. 3rd, 4th and 5th are easier, but still don't engage sometimes. When shifting at exactly 3500 RPM it works just fine, and for 4th, about 3200 RPM works best. Does anyone know what's wrong? Do I need a new clutch? or a complete rebuild?