soo i just realized i have to do my 30k miles since previous owner that i bought it from didnt do it. Im at 36k right now and started feeling when i shift from drive to reverse or visa versa (yes i have automatic) that it pops (car moves a little not how its suppose to) a little which sucks and i have no idea what that might be. Anyways i was goanna try to do the maintence on my own but i really dont know much about the engine and wouldnt wanna mess anything up. Im down to do it myself if i had help from an expert but since i dont and since its first time the cars probably getting it fluids changed i thought id play it safe with nissan in kearny mesa to do it for me. They qouted me $360 ish for everything vs. Infiniti qouted me 702 (lol?). Do you guys think this is reasonable? plus any ideas on what the problem is when i shift?

p.s. i did do my search on forums and did my reading just thought id ask the fellas from sd to see if you know a better place to get everything all checked?