Prerunner

I'm new to this thread. Have looked many times as a guest for very helpful information.

Here is what I have- 2008 Tacoma quad cab, 6" lift 35" tires. Lift spindle and spacer, add a leaf and blocks

1} Shudder from driveline when take off from a stop. Already have the spacers at carrier. No vibration above 5mph or above, um 125mph.
2) Before lift, when I come to a stop, there is a "bump" in the rear suspension. Lubed springs but still occurs. AC is off, but worse when it is on. Have ridden in other Tacomas and same issue. What is this?
3) How does engine performance affected if the backpressure is released by removing the 2 cats behind the o2's? There are 4. What is the purpose of these? Scavenge?