In an earlier post I asked about anchoring near brush piles. Clearly the consensus is "don't!" And thanks Ken Gaby for the detailed explanation why.

Maybe the reason I've been thinking I need to anchor is because my TM isn't running right? It's a Motorguide Brute 767, 12/24 - probably the original on my 2001 G3 18-ft aluminum. Even on 24 volts it doesn't take a whole lot of wind to send me to the cockpit because it won't pull the boat directly into the wind at all. And in calm water, it's not moving the boat as fast as a smaller 12V unit I had on a Bass Tracker years ago. The motor on this rig is heavy, I suppose: a four-stroke (4 carb) Yamaha 100, but something doesn't seem right.

Do TMs lose power as they get old? Batteries are definitely good. Nothing stuck in prop.

Check the motor to see if it is really getting 24 volts to the unit. Measure the voltage right across the two leads at the motor, not across the battery. High resistance anywhere in the battery positive or negative line will result in poor performance. High resistance can result from corrosion or loose connections. If the motor never performed as it should it may have been installed with too small wire. Fuses and connectors are also prime candidates for voltage drop.

I'd say something is definitely wrong. Smithhaven gave excellent advice. That motor should have plenty of thrust for your G3. Motors usually don't go bad, however, if all the above checks to be good, I'd look at the TM itself. Might pull the prop off and make sure there's not line wrapped on the shaft.
Boris Marine Electronics is a good place in your area to have someone look at the TM.