96 MAXIMA has trouble starting and wont stay on

[To the Max!]

Hi everyone I'm in a world of confusion and I'm hoping I can find help here. I have a 1996 Nissan Maxima that I just finished swapping the engine on. I rebuilt the replacement engine with all new gaskets and sealants. I torqued everything down to sepcs and from what i know timed the chains right. I used a Chilton book and watched a Lot of Youtube vids. If I'm correct the timing should be set on the fourth stroke (exhaust) TDC and the colored chain links are to match the the marks on the appropriate sprockets that are also set 180 degrees from the block mating surface. So after I rebuilt the engine I rotated the crank multiple times to make sure it didn't lock up. I dropped the engine connected everything back up and hooked all coolant and vacuum hoses and sensors together. I double and triple checked everything before I tried starting it up. So the car will crank but only start about half the time. If it does start it rough idles around 500 RPMs or so then dies seconds after. Also if it turns on and i try gassing it to keep it on that seems to kill it instantly as well. Here are some of the things i did so far:

1. replaced fuel pump
2. replaced fuel regulator
3. replaced spark plugs
4. replaced spark plug boots and coils
5. replaced crank position sensor

The coil packs and camshaft position sensor worked fine on the old engine so i switched them to the new engine as well. The power steering, transmission, and coolant fluids are all around half full, in case i had to drain em all again but the oil is full.
Also I was wondering if I needed to reset the computer because some people mentioned i might have trouble with that but i can find no info on that anywhere. Please help me find out what I'm missing so I can fix it and be happy once again. This is my only everyday car and I'm hurting everyday that he's down.

[NutriaforBreakfast]

Check fuel pump relay
I think it is near the drivers seat under the fuse box and to the
left

Double check throttle position sensor

I think there are 2 cam or crank position sensors as well to check
(REF) and (POS)

Good luck-don't know if i could make it start either