The Robins snatched an undeserved point with six minutes to go with sub Damien Spencer fired home after Anthony Willaims failed to hold a long range shot in difficult conditions.
Speaking after the game Slade bemoaned his sides lack of ability to finish teams off.
"We had an opportunity tonight to climb the table and we haven't done that," he told the Grimsby Telegraph.
"The dressing room atmosphere is like a defeat - that's how bad the players are feeling.
"We were given the chance to get off to a terrific start when we got the penalty so early on, and that would have given us a good platform.
"Unfortunately for us Thomas (Pinault) didn't take that but we still kept on and got a good goal from Andy Parkinson to set us up.
"The problem is we didn't go on from there - when we are 1-0 up we have got to finish teams off."