Do you have a 48" or 54" inch bottom? The narrow bottomed boats are more work to move. You should also check to see if the boat is properly balanced...if your stern is riding too high/low, then boat won't respond well.

My buddy had an Alumaweld 16x54 and I thought it rowed like a tank. It had all the fancy boxes and trays and stuff, but it was a slug.

I have an old 16x54 Wooldridge without all the crap in it, and it's much easier to row and move around than my friend's Alumaweld was. Looks pretty much like it did in 1973, which is a nice thing about tin boats.
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She was standin' alone over by the juke box, like she'd something to sell.
I said "baby, what's the goin' price?" She told me to go to hell.

Bon Scott - Shot Down in Flames