Timing Belt tensioner and Diagrams?

Timing belt broke and wanted to know if the right timing is the marker on the block match themarker on the gears also if you could give me from start to finish instructions on how to time it

I have been struggling with P0030 code (multiple cylinder misfire) and have replaced literally everything.
Finally removed front of engine, put crankshaft at Top Dead Center, one camshaft pulley the timing marks lined up perfectly, the other would line up if I moved the crankshaft to 15 degrees before Top Dead Center was exactly one tooth, so I fixed that and it runs way worse.
Took it apart again, rotated the crankshaft and all marks line up perfectly.
The camshaft that was off was not for cylinder number one.

Do I need to re-time the engine anyways?

This is a motor I got off JDM auto
After install it has very low power and horrible gas mileage.
Kept throwing P0030 misfire code.

Put on
New Distributor
Plug Wires
Spark Plugs
PCV Valve
Crankshaft Position Sensor
O2 Sensor which was bad
Timed it properly with a light

Still threw the P0030 code

Decided to check timing belt, right side camshaft gear was off one tooth.
Adjusted and marks line up perfectly every time after a few manual rotations

Now it runs worse, ECM keeps moving the idle up and down.

All the wire harnesses fit perfect.

Engine came with alternator and power steering pump reversed hence it was the same engine but probably off a different Nissan Model

I will do compression test but starting to think the ECM is not compatible,

I did disconnect both exhausts at the manifold to make sure catalytic converters were not clogged - no increase in power

Engine compression tomorrow morning.
I believe Nissan check the Pressure but I will again.

I do have it running 80%, when I adjusted the timing belt I was off, so I put it back re-timed the engine and runs better. I would say 70%-80% power - so gutless on hills and requires so much pedal to get it to down shift - or just make it up, full pedal and it takes right off.
Down to a P0031 code, at least I have a cylinder number.
Tried a new TPS - no luck.
Was swapping #1 and #3 fuel injector to see if it would switch to P0033.
Dropped the Aluminum cap that holds injector in place - no-where to be found after 2 hours
looking, LOL.

This truck I changed timming belt now give me code po2340 and po328 please help, truck running good, but engine light on.
Best regards

Asked this question earlier but was waaaay off on car description. I have a 2001 Nissan Xterra V6. Please confirm that it has a timing belt and not a timing chain. What is the suggested mileage to have a new belt installed?

Thanks! Just talked to Nissan dealership and he said considering the year of the car (not just the miles) I might want to have it changed before it hits 105,000 miles. Is this a true?

Since its about 8 years old with only 62,000 miles do you suggest I replace it now?

Engine Mechanical problem
2001 Nissan Xterra 4 cyl Two Wheel Drive Automatic 100k miles

The Nissan 100,000 mile service includes replacement of the timing belt and runs about $1100. If we perform this service can we expect to increase the car's life significantly? The car runs well now and has been very dependible.