When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I can sympathize though as I couldn't get my old car into my garage due to the kit. Just get some wood planks and place them strategically so you have more clearance.
Kinda interested to see this as I have a garage with the lip and steep incline nothing over the top but my rear is slightly tucked and I have had no issues as to clearance on the diffuser. Was the diffuser mounted to low possibly....?