I hope someone who actually owns a 328 chimes in. I'm surprised you had timing issues. Some stupid questions: How often do you use the machine and are you threading the bobbin thread correctly? IIRC your machine uses class 66 bobbins. The bobbin should go in with the thread counter clockwise and the thread pops into a little notch in the side of the bobbin "case". If the thread isn't in there you will have no bottom tension. Please forgive me if you already know all this. I just don't know how familiar you are with your machine and want to cover everything.
Can you see a loop on top or does the bottom thread just show but the stitch is basically tight? If you have an actual loop then the problem is in the bottom. Compare the bottom tension on the 328 to a machine that is working well. The tensions should feel about the same. It could be you need to take the bobbin tension spring off and clean behind it. If there's lint or a piece of thread in there it won't allow you to adjust the bottom tension properly. If everything checks ok on the bottom but you're still having trouble take your top tension apart and clean the disks thoroughly even if they appear clean. If everything is right you should be able to get a good stitch with your top tension set around 4 or 5.
Tools for Self Reliant living has excellent tutorials on rebuilding and adjusting sewing machine tensions. Sorry I don't have the link saved.
I hope this helps,
Rodney