Canned vs frozen clams in recipes

Hey folks. Looking for some experienced counsel here. I have used canned clams for years with good results to make linguine with clam sauce (white and red). I can simmer the sauce as long as I want and use chopped and whole canned baby clams with good results. So extrapolating from the fact that frozen vegetables taste closer to fresh and produce better results than canned vegetables, I figured frozen clams would work better than canned. So when they went on sale at a local farmers market I bought about 6 lbs of shucked frozen raw clam meat.

When I went to use the first pound, the clam pieces were tough after stewing for just 5 minutes. I tried stewing them for 30 more minutes and that didn't make them any more tender. They must put some mojo on the canned clam meat to make them immune from that sort of thing. I have read articles stating not to overcook fresh clams.

Can one of you experienced clam cooks tell me the secret to using frozen clam meat and how to either keep it tender or how long to cook it to tenderize it? Am I making a mistake using fresh clam meat in my Italian clam sauces? I was hoping to use it in a paella but I know that would produce the same result. Thanks in advance for any advice!