2000 Ford Windstar 3.8 (200k plus)

Hey Guys Im new to ETCG and im not sure if this is the correct forum so cut me some slack. BTW I am A certified tech and also own/operate A small shop w/ A partner. 2000 windstar (200K) came in today with horrible misfire (cyl 2&3). The wires for cyl. 2&3 were burnt, split open & obviously bad (plugs & wires were original w/ 200k plus miles). I replaced the plugs, wires, fuel filter, air filter, cleaned throttle body, and OFL. I cleared the codes test drove the van and all was well. 2 hours later I was moving the windstar and while in reverse I noticed a slight miss so I took another test drive van ran great. Now if you load it up in REVERSE ONLY at about 1800 RPM it has a miss but under normal driving conditions its fine!! I replaced the coil pack with 2 different test coils, checked for cracked plugs, checked for vacuum leaks, checked & cleaned EGR & passages, checked compression,all were OK/normal. Did power balance test at least 5 times with a scanner & a sun machine. Power balance showed very, very, very slight drop offs on cylinders 2-3-5 intermittently or at random. Im pulling my hair out!!!! HELP!! PLEASE!!