2001 Ram 1500 truck, now has 318 engine, if changed to a 360 will I need to also replace the computer or will the 318 computer work?

Ummm....yes.

if going from 318 to 360 in 2001 truck and 360 is also magnum, only need to make sure you use the 360 flywheel/flexplate. i would try the 318 computer 1st but also get the 360 computer also if avail. if 360 is not a magnum, it may not have provisions for crank sensor on block.

I would have guessed something is different with the bigger displacement. Altho maybe that's something the different sensors would pickup and account for to add more fuel etc..

Bigger injectors? Different tune?

I'll bet the factory didn't use the same computer, but I am not going to look it up either.

If my fuzzy memory is correct,
the OBD-II computer system of your 2001 5.2L V8
uses Siemens made 23.2 lb/hr fuel injectors at 45 psi

Your 5.2L V8 2001 computer will run a 5.9 V8 OK in everyday driving as it “learns” to increase the short and long term fuel factors,
but even after fully learning,
at wide open throttle on the 5.9L
your air to fuel ratio will be leaner than the factory 11 to 1 ratio
and you might get pinging,
perhaps even damaging detonation
especially if running 85 Octane/AKN gasoline.

1994 to 1995 Magnum 5.9L V8s have the older OBD-I computer system
but do have bigger capacity fuel injectors ( but 35 psi fuel pressure was the spec back then)

Your 2001 model fuel injectors may have a smaller electrical connector. Adapters are available.

Put a 2004 5.7 Hemi in and gain 6% fuel economy

The oil pan on 318 and 360 magnums are exactly the same.

Motor mounts on 318 and 360 magnum are exactly the same for your application, the mounting ears are different but your motor mounts bolt flat to the side of the block and do not use those ears.

The computer is programmed slightly different but will run just fine, actully better as the 318 runs very rich at WOT, the 360 will suck in some more air to make it closer to stoich. Part throttle will trim to match the engines needs once the O2s starts working and is close enough during warm up you will never notice the difference. The 318 seems to use slightly more advance under most conditions especially if your 5.9 computer had a death flash.

The flex plate and whoremonger balancer are different, externally everything else bolts up exactly the same.