I've seen 3.55s leave 5.0s with 3.73s or 4.10s in the 1/4 due to traction issues. A battery relocation (taking 30 pounds off of the front with the battery is like adding 50 where it's most needed) and higher profile drag radials as olehead suggested are your best options IMO. Which Eibach springs do you have? Stiffening the suspension will generally hurt out of the hole traction due to lack of weight transfer. An MGW or Barton shifter may also help considerably.
2007 Mustang GT 302 stroker 6060 swap, 3.73 gears, Hidden Hitch Receiver, Barton Short Throw, JBA LTs, Borla Touring Axle Back, Lito tuned SCT X4. BMR SP009, Bilsteins, J&M CC plates, J&M LCAs. 4 Piston Brembos
DOB GT450 with VMP Gen II 2.3 TVS | 13/14 GT500 HE & IWP | GT500 hat & DW340s | FRPP 52lb | CMS Stage 2 Blower Cams | Comp 113 Springs & Retainers | 8 rib conversion | Track Spec GT500 Vents | PTFE Heat Barriers