I have used a lot of Dayco belts over the years and never had a problem with them.
As to your fuel, you probably should add a heavy dose of Diesel Kleen or a similar good fuel cleaner product to the tank to help clean things up.
After you run it a bit with the fuel cleaner you probably should change the fuel filter....
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount98 Dodge Cummins 24 Valve