I received my trim pots in the mail and set up the circuit diagram you provided omitting the LED's, and for some reason with R1 set to 10K, no matter R2, the motor behaves as if it were plugged directly into the power supply. I checked the pots with my multimeter and they are performing as intended. I tested R2 values using a variety of different pot values, and also tried with standard resistors. Am I missing something obvious here? I have tried about 6 different schematics at this point. Could my TLC555CP be the root cause of these repeated failures? I am at a loss. I have tried 5V and 3.3V.

Try to simplify the problem. I suggest using an online 555 calculator to find which components are needed to set the frequency to to a comfortable 1Hz with a 50% duty cycle. Use an LED and watch what happens when you adjust the duty cycle. Next change the frequency to 100kHz and watch again. It's best to use a scope but a multimeter can also be helpful. At low frequencies, you'll see a clear transition from 0V to V+ whereas at high frequencies (100 kHz+), the output will appear as V+ / 2 (for a 50% duty cycle and with no load). These tests will help confirm if your 555 IC is functional. If all is good up to this point, the problem lies either in the driver portion of the circuit or the motor itself.

https://ohmslawcalculator.com/555-astable-calculator

 

Do you have an oscilloscope

Unfortunately not, a bit out of my budget at the moment. I am going to try to adjust the values and frequency to blink an LED to make sure my components are still functioning as intended. Hoping this will help me identify the root cause.

 

These tests will help confirm if your 555 IC is functional

Saw this after just posting a reply. Thank you for the suggestion, my brain was headed this direction but not with a completely clear path. Will give this a try this evening.