I have (3) Spektrum SR300 Receivers which connect to my DX3S.

They are in my Traxxas Slash, SC10 and my Jammin SCRT10.

I am noticing some distance issues in which I lose the truck.

I think it might be because the antenna on the receivers is not fully extended. I have them in the original receiver boxes that came with the cars.

The traxxas for example the antenna goes unterneath the receiver box and then out the hole made for the receiver antenna. When I do this with the Spektrum receiver antennas, they seem to be really short.

Any suggestions?

I'm with you on this. I run the slightly older DX3 with SR3000 and it has less distance than my Futaba 3PM 2.4. From what I've read this is "normal" but still anyone have any ideas on how to increase the range?

I put in a receiver in my slash yesterday and I went about 75 feet away and it became twitchy and unresponsive.

Ok thats a little excessive..... Mine can go a few hundred feet and then enters failsafe. Check your batteries.