Technically, you're overloading it. However, those cheapass lighting transformers ratings are dubious to begin with. You should be prepared that it doesn't even support 44W.

What type of light bulbs are the 20watts, replace those with LED bulbs problem solved.

Yes you are overloading it and depending on the distance traveled you will lose rigidity on the line.

RL Relication- I thought about relamping the two 20 W lights with LEDs, but then I realized I would end up with a total of less than 15 W for everything, and I’ve always heard that a low voltage lighting transformer should have at least 60-80% utilization of its capacity.

Are there multiple taps on your transformer output, or is it just a single 12vac?

The transformer is a Malibu/Intermatic model 44T with A, B, and C taps. The manual for it only shows the wiring hooked to the A and B taps, with the C tap reserved for hooking up photoelectric.

How far is the run from the source?

Furthest lights are about 40’ from the transformer, and I’m using 14 gauge wire.

I would try lowering the wattage on the 20watt bulbs.