IP choices

[BUZZ]

I ran across 2 IP's.

I had both inspected for contamination, both were clean.
I had them both calibrated. Both pumps tested in spec.
IP #1 is model 5429 date code 8/20/98

IP#2 is model 5521 date code 1/25/01.

Besides the obvious 5521 being the newer of the 2 and I have compared the calibration specs to to the test proceedure. Only minor differences in the pumps output readings.
Which Pump would you keep as a spare?

My experiences are when buying what appear to be warranty R&R IP's, worked out for me.
I suspect the PMD or other vehicle problems for these 2 pumps being replaced.
I should point out that the top cover on #1 was leaking, the seal was out of grove. Which probably drove the replacement.
Buzz

[More Power]

If only keeping one, I'd keep the newer... Stanadyne made incremental improvements throughout the life cycle of the 6.5 DS4. This is partly what drives the model number evolution - same pump, same application, but with minor mods and new model numbers..

Jim