Replaced alternator and battery car will run fine for a few mins then lose all power when it does do what its doing u can push throttle in park and accelerates fine but then u put in reverse or drive still running just want throttle up put it on freinds computer but didnt read any codes it was not a nissan computer though he said something about take it to nissan dealer and have them flash the computer just wondering the next step I no a dealer trip will be expensive any ideas or something I could do myself or leave to experts thanx
Wow. Did you proofread that huge sentence? With no punctuation it can be read at least three different ways. "Lose all power" can mean a lot of different things but since you referenced "alternator" and "battery", I'm guessing you mean you're losing electrical power. One test you can do is to measure the battery voltage while the engine is running. It must be between 13.75 and 14.75 volts. If the problem acts up intermittently, be sure to do that test while it's occurring.
If you have an indication things inside the car are going dead intermittently, look at the two smaller battery wires. The negative one will be bolted to the body and the positive one will be bolted to the under-hood fuse box. Be sure those nuts are tight.