Dryer makes loud clunk and struggles through cycle

my dryer makes a loud clunk when I start a load and then the engine labors. we have it all taken apart. The belt seems okay. what else should we check. Homer, Alaska

Here are your parts
Replacement parts for General Electric DSXH43EA2WW Electric dryer | AppliancePartsPros.com

Check the rear drum support bearing (Item 1201 in Section 3).
Note: Most of the parts are available individually.
When re-lubing be sure to use a high tempo grease.
There should be an access panel at the back to let you remove the ball bearing (Item 1205 in Section 3). Watch this little sucker as once released it likes to play hide and seek and can waste a lot of time looking for it.
This little ball bearing reduces static electricity build up in the drum/clothes.

Check the motor mounts to be sure they are not loose also check the motor bearings for slop.

Check the front glides (Item 1124 in Section 3)

Check the vanes in the drum are tight though this would not cause the motor to labor.

Check the drum seals (Item 1221 in Section 2)

Check the blower wheel (Item 1310 in Section 4) for ant foreign objects.

Also the belt itself and the idler wheel.

This would be a good time to clean the interior including the blower wheel.
Also your vent system.