I have significant experience with the powergear electric jacks. A couple facts I discovered in the course of my pain, was the jacks should not be greased, that attracts dirt which causes the shaft to bind. clean the shafts and spray with transmission fluid which significantly reduces the dirt issue.
I finally realized after replacing many shear pins that there was a pattern to their failure.
First be sure to deflate the airbags prior to setting the jacks!
Second when set at a site for more than a day the chance of breaking a pin increases because the ground settles and the jack binds. If you re-inflate the airbags before retracting the jacks they take some pressure off the jack shafts, reducing the bind and that stopped my breaking shear pins.
Last item is NEVER let the jacks extend to their full length, use blocks under the jacks to fill the gap. It should be noted that the blocks, if large enough also significantly reduce the sinking into the ground.
By the way, the shear pins are available from Fleetwood Parts, and generally I've had fast response in getting them. I actually kept 4 onboard, just in case. I do have a full powerpoint presentation on how repair the jack if you need it.
Please feel free to call if you need further help.