i'm just gonna attack the backfiring. with the mods the previous owner put on, you're running rich. sooo, what you need to do is get your EFI adjusted to the new mods. so either find an existing fuel map and take it to the dealer and tell them to adjust it for you, or pay for a dyno fuel mapping and get it custom adjusted. the choice is yours. good luck.
i'm gonna take a few guesses at the other problems, maybe when your shifting, your at a higher rpm ( b/c your just checking for the correct gear) which doesnt give the synchros enough time to do their job thus making it a tough fit. so i dont think its actually doing any damage, but i'm not a tranny expert. and as for the suspension...guess and check?
i'm gonna take a few guesses at the other problems, maybe when your shifting, your at a higher rpm ( b/c your just checking for the correct gear) which doesnt give the synchros enough time to do their job thus making it a tough fit. so i dont think its actually doing any damage, but i'm not a tranny expert. and as for the suspension...guess and check?