What gmsemel and Rocky posted about shorter and stiffer leaders is spot on.
You mentioned using an unknown tippet material and that's the first thing that needs attention. Since panfish aren't terribly line shy and especially when using poppers go with a relatively stiff tippet material in 6lb or 8lb test like Maxima. Keep the tippet short ... say approximately 20" and the overall leader under 8'. A good option would be go to a fly shop and purchase a bass or saltwater tapered leader that's made to turn over heavy flies.
Another thing that can affect how the leader turns over is the fly line to leader connection. It has to be a relatively even transition in stiffness as opposed to a uneven connection that can hinge. One way a hinge can occur is when you have an old knot that has worn through the outer coating on the fly line. If it hinges it won't roll over smoothly or efficiently
A last resort (and I do mean last because you can't undo it) would be to shorten the fly line itself. Bass bug tapers have a shorter taper from the main running line to the terminal end. They're designed to help turn the line over when casting heavy bulky flies versus a longer gradual taper (trout taper) that lays the line out smoothly with less slap on the water.
The only reason I'm mentioning this final option is because you have a 5 wt line which is marginal for turning over a heavy or wind resistant flies or poppers. Look at your line and see how long the terminal diameter is. A trout taper is usually in the 4' range. If it's 4' cut 12" off.
This isn't the best pic but it does show the difference in a gradual tapered fly line (double taper) vs a shorter blunt taper (saltwater taper) which is designed to cast heavy bulky flies.
Lastly what gmsemel posted ...
"To load a rod you have to get the fly moving first, try starting your cast with the tip of your rod close to the water, and no slack in the line from your rod tip to your fly"
This is what sets up the forward cast. You said you know how to cast so don't take offense.
One of the most common errors I see is starting the forward cast too soon. You have to wait until the full length of the fly line is laid out straight on the back cast (wait until you feel the tug) and then punch it. This is the key to generating enough line speed and energy to lay out the line and roll it over.
Hope this helps.