Hi/Low altitude CPS???

Autozone lists a hi altitude and a low altitude CPS, the hi alt one is ~$40 the low is ~$25. What is the differance and which do I need? Does the H/A one advance the timeing? Why is it more expensive???

BTW, this is for a 2.5L TBI.

The HA does advance the timeing, I seem to remember that the dealer carries a HA 'kit' but it is more than the AZ one, ~$60 IIRC but cheaper than the stock Low A one. I guess it's a toss up between the dealer and the aftermarket, things like slaves, clutches, thermostats I would only buy OEM/dealer as the aftermarket seems to have a higher failure rate. Besides, I though all colorado jeeps came with the HA models already as stock ??

CO jeeps do come with HA stock, I need to replace mine.