RPM troubles

[Venom1515]

I have 420a auto. and I did a complete rebuild from the crank to the head. I replaced the pistons, rings etc. now i am driving it (not hard) and I noticed the rpms are really high like around the 3000, 4000 range when I go 60 or so and at idle it drops from 1000rpm to 800 and also sometimes when i start it backfires (This only happened once) what could this be and is the idle thing normal for break in time. The engine has 60miles on it now.

 

[Venom1515]

I have 420a auto. and I did a complete rebuild from the crank to the head. I replaced the pistons, rings etc. now i am driving it (not hard) and I noticed the rpms are really high like around the 3000, 4000 range when I go 60 or so and at idle it drops from 1000rpm to 800 and also sometimes when i start it backfires (This only happened once) what could this be and is the idle thing normal for break in time. The engine has 60miles on it now.