1) dunno
2) It's your tranny kicking down to 1st after you stop. Programmed to do so for several reasons. A new, stiffer or anti-wrap-leaf equipped spring pack may reduce the thump a bit, but not for the reasons he suggested and it's a pricey solution to a minor annoyance (unless you wanted more wheeling ability too).
3) Try changing gas brands. Also, have you run BG44K through your system regularly? Try that, you may have some carbon buildup. My 5VZ-FE loves just about any cheap regular I put in it, but mine is out of a '96 and has seen BG44K regularly.