How Often Should I Change Copper Plugs?

[2500hdee]

2001-GMC-2500HD.......Truck has ran like a champ since I swapped from the iridiums over to NGK TR55's; I know however, they'll need to be changed more frequently. I'm just unsure how often. Thanks ahead of time for your input

[ryank1]

Standard plugs usually need to be changed approx every 30k.

[2500hdee]

Thanks

[Judge Smales]

2001-GMC-2500HD.......Truck has ran like a champ since I swapped from the iridiums over to NGK TR55's; I know however, they'll need to be changed more frequently. I'm just unsure how often. Thanks ahead of time for your input

What did you gap the TR55's at?