NEED SOME HELP (wierd stuff happening when i put the petal down)

OK here is the deal... I have got a 91 civic hb that come with the extremely unattractive DPFI,... BUT WAIT!!! i had a local shop do the multi point swap on it with a jdm si manifold and 91 SI computer . Every since the swap was completed...
1.) If i hold the idle aroud 4000 or so it is really unsteady, and rough...
2.) Every once in a while, if I rev the engine up and let it rev down,and do this over and over (where it kind of sounds like a rev limiter, "to get you on the same page as i am" ) It will backfire through the intake manifold : not cool
3.) Last major thing is if i run on the interstate (it is a 4 speed) and tap 3rd to the limit and shift to 4th, it almost feels like it runs out of gas for a split second right as i shift and step back on the gas. Basically it almost dies for a split-second...
WHAT THE HECK IS GOING ON???ANY SUGGESTIONS OR COMMENTS???

for the back-firing, replace the PCV valve on the manifold. I picked mine just the other week at Autozone for $2.88, It's supposed to stop backfiring. Also, the timing might be off.

Sounds almost like they might have mixed up something with the MPFI swap. Read through this thread (http://www.automotiveforums.com/vbulletin/showthread.php?t=292359&highlight=eacv+plug) and try to see if maybe that's it... (something about EACV and IAT plugs looking alike and plugged in wrong)... Also, are you getting any codes?

timing. it was rough one mine to

yeah it is flashing codes 1 and 15 i think or 13 what do they mean???

code 1 is o2 sensor. code 13 is atmospheric pressure.
code 15 is ignition output signal.

Yeah problem number 3 is due to a bad o2 sensor or a disconnected one-which happened to my friends protoge.---connected it securly and it works fine!