The problem with going to a 3V 5.4L is that the PCM also controls the transmission, so you'd have to swap that also, since the 3V engines have 5R110W transmissions instead of 4R100s (unless you have a manual transmission),

Swapping the PCM and installing a 2V 5.4L would work, but you're not gaining anything. Mileage may be a little better, but it won't be enough to justify the swap (especially when towing). Ask any of the guys here, I am a huge fan and cheerleader of the 5.4L V-8, but what you propose makes no sense.

Consider this: The 5.4L V-8 is basically the same engine as the V-10, just minus a few cylinders. If your work routine isn't cutting it with the V-10, the V-8 will give you as much (if not more) trouble, since it will be working harder with the same load.

Triton V-10s are solid engines. You should not be experiencing these problems. Oil pressure problems and broken valve springs are a sign of bad maintenance, bad repairs and/or hard driving. Before doing anything I would take a hard look at why you had oil pressure problems at 50k, why you lost a valve spring at 100k and why you're not holding oil pressure now.

What oil and filter do you use?