It's almost impossible to determine what the main cause is for the change in distance is. You changed club heads, lowered your loft on the club head, changed from (I presume) a graphite shaft to a steel shaft and from a regular flex to a steel flex. Every one of those changes will have an impact on accuracy and distance.

A stiff shaft will help out a fast swinger by keeping the path a bit straighter, but a loss of distance is also factored in.

A steel shaft is a bit heavier than graphite, which will also help keep you a bit more accurate, but with a loss of distance.

Last, you changed heads! How can you copare distance then and now if you use two completely different heads?

The decrease in loft will also factor in a bit - the optimal trajectory for a driver is 14* - 15*. Depending on the kick point in the shaft, this will vary from club to club.

It is impossible to pin point the exact cause but I gaurentee everything mentioned above had a bit to do with it.

If you want to know for sure if it's the shaft or not, switch shafts with the other club and try both shafts in both club heads.

__________________
Gord

Quote of the month:
"It's easy to see golf not as a game at all but as some whey-faced, nineteenth-century Presbyterian minister's fever dream of exorcism achieved through ritual and self-mortification." ~Bruce McCall