i have a 94 z28 with the 4L60E trans. 4 speed auto with 1st gear lockout removed... recently the trans was professionally flushed and everything was fine for about a week, now it has a hard shift from park or neutral to forward drive gears, reverse is fine, all gear seem to shift fine when in motion until its time for the drive to overdrive shift, it tachs out on the interstate and doesnt go into overdrive, but when its in drive not tach'd out, and you floor it, it downshifts ok... i have read its possibly a shift solenoid that runs off vaccuum pressure or possibly the pressure block itself being stuck? or even the torque converter......anyone with these same problems or know anyone with em and a solution or troubleshooting checklist? or would i be better to just take it to a transmission shop and have it looked at? only thing i can really find out beyond that is everyone saying junk the 4L60E and do a custom TH-350 swap with fabricated overdrive gear..dont have that kind of cash for that, or even a new transmission seeing how they run average $1200 not including labor.. need help!