Bought first pair of back rotors and realized I ordered the wrong ones. I should be getting my new rotors/pads for the rear today or tomorrow. I'll have them on by the end of the week and update.

 

Yep, i remember when i had pulsing braking when slowing down, where i could also feel it by holding the shift ****.
Once i replaced all four rotors the issue was gone.

 

may to rebuild your front calipers.

 

If you have replaced the front brake pads and front rotors, take a rear wheel off, and check those rear calipers. The bolt on the top of the caliper takes a 19mm socket. Loosen it and see if your caliper will rotate towards the rear of the car. It should pivot rearwards so you can slide the rear rotor off. If it doesn't it is rusted and you can't get the rotor off. Take a 2"x2" piece of wood, maybe 28 inches long, and use the leverage of it to pry the caliper backwards at the top. I wedged it between the caliper and the rotor and pry, not crazytown destructive pry, because if it doesn't move, you will need someone to heat that pivot pin to loosen it.

If you get the caliper rotated rearwards, the Rotor slides right off. Its an interesting rotor, You have drum like brake shoes under that center section that are for your emergency brake. So don't let no one beat on it, place never seize in that center area so the rotor never rust solid on there and won't come off.

See if your rear brake pistons on that caliper will allow you to compress them easily. If you must use a C-Clamp, and it is hard to crank it in, the calipers maybe frozen and causing that pulsating, when you press the brakes to slow down.
I have had the rear caliper on the passenger side go bad twice, and I have 60K miles and only got in the salt spray ONCE ! I replaced it at 48 K and now again at 60k, BS.
Its annoying, it will cause that 'pulse' . Mine wasn't in the brake pedal, you feel it in the seat .
I have to replace the rear pads this time. You know what is annoying, Sewell Lexus not having their parts store on line ! They had an excellent website back in the day.
Check those rear calipers.
best regards
greyhound

 

If the pulsing is in the wheel = front brakes
If the pulsing is in the brake peddle and not the wheel = rear brakes

 

UPDATE: I changed my rear rotors and pads on Friday. It's been 3 days of driving and I have had zero issues.