Step 12.1. Clear world cache:

Click Show then Downloads.
Right click in the white space and select empty cache.
Select the desired avatar from the Avatar menu when finished loading.

Step 12.2. Scale - Adjust the scale in the "Save with options" window in Accutrans.

Textures - Make sure all the images are in the right folder and applied to the body parts correctly.

Laggy - Model may need to be optimized better to have a smaller filesize (Less than 300kb is good).