Pressures should be checked using engine vacuum as your guideline. I'm not going to post the entire chart as it is quite comprehensive. At idle in drive, low, 2nd with 17" or more of vacuum @ 29.5 barometric pressure] there should be 51-66lbs of control pressure and 72-108lbs in reverse only. Next pressure check is done at 15" vacuum @29.5 BA/HG, press. should be 70-78lbs. and so on. All the way down to below 1.0" vacuum where press. should be 157-172 lbs [drive, 2nd and low gear] reverse should have 230-252lbs of pressure. This is specification for a STOCK built C6, not with a shift kit or any other valve body modifications. If you have the pressure you have found I'd be looking into the input shaft, broken, stripped splines or any other mayhem in the input shaft, forward clutch splines, etc. Not having reverse tells me the forward clutch could still be functioning, maybe not 100% right but when only the forward clutch fails the trans will still have reverse as rev is the only "in gear" position that does not engage the forward clutch, hence the name "forward". Most of the forward clutch failures I've dealt with are broken or hard seals that won't hold pressure. When that happens the forward clutches go south very quickly as they are slipping. My comment regarding "At low idle there should be 60-65lbs press." was a guesstimate that should have merely proven the front pump was still working. IMO, You should pull the trans and with the converter removed grab hold of the input shaft and pull it out as there is nothing holding it in such as a snap ring, etc. Let us know what you find.