try to do tune up(check wire,sparkplug,distributor),if still have problem,adjust idle speed.40迈时,如果踩油门大一些,车就发抖,速度上不来,必须慢慢加油,lots of nissan old car like this.you can check gas filter,adjust ignition time,but you can't fix it completely.速度到65迈也就到头了,速度上不去,65 mile about 105-110km,for 12 years old small car ,I think almost max.my car(93 nissan sentra) never run over 120km.