Wobbly Av8r's post in satellite was marked as the answer
Two immediate possibilities; the first would be reentry causes comm blackouts option is checked, the second may be that the satellite may be on the other side of the planet blocking a connection.
So, what I've found while attempting to tackle the same problem is two-fold: 1) Getting the S-IB to separate cleanly while retaining the interstage ring, and 2) Getting the interstage ring to leave the rocket "nicely".
Given the conversation about your choice of engine, I would humbly suggest you may be over-fueled... when I created my Saturn V Doppelganger, my booster tanks were more empty than full - and I used the more highly Apollo-like pieces to recreate a reasonable facsimile, as I'm sure most folks would prefer.
Rather than try and describe little details (and thus bore you and/or anyone), I'll just post it to kerbalx: https://kerbalx.com/Wobbly_Av8r/Apollo-Saturn-V so you can get some ideas for how you might solve your construction issues...
The solution I found for the interstage ring separation was to detach the S-IB with a TD-50 decoupler, the interstage ring being formed by a fairing which is not 'deployed' (as most fairings usually are) but 'staged' because it is attached to the S-IIC by one of the nodes of the engine plate upon which the 5 RE-I2 second stage engines are attached. One last note here - the T-50 Structural Tube section that I've seen used for this section is very 'draggy' and difficult to get to separate properly, hence the solution I chose.
While your orbit parameters looked pretty much right on in the top post / image, because the orbit is slightly elliptical, it doesn't appear that your Ap and Pe are in the same location as those of the orbit it was expecting... so I think the easiest solution would be to make a maneuver node at one of the two locations where your orbit crosses the specified orbit and perform the proper "Radial In" or "Radial Out" to "twist" the orbit into place. [Edit: One of the crossing points is at the (visual) 2:30 position relative to Kerbin in the top map image and would require a radial out burn. If your other parameters of Ap and Pe are still "on target" you should only need a radial burn]
That's what it appears like to me, but I could be mistaken. At least check into the maneuver node to see what's possible...
Good luck!
