merc sprinter wheelstuds heating up

[evolutiontransp]

hi folks after 23000 miles this year with only a wheelbaring stopping me
ive got a problem with wheel removal
up until a few months ago wheels came on off no hastle
now they wont budge
now all 4 wheels are solid and need took off with a 6ft torque bar
anyone any idear whats causing this and solution please

 

[Sp!ke]

Who tightened the wheel nuts last time they were done up and were they torqued up correctly?