From my understanding of things, a 5800gph hammerhead pump should be supplied with at least 2" diameter pipe. That should flow about 5400gph to it.
If your pump is restricted on input, it will cause cavitation which will show itself as noise, heat, and usually fine bubbles in the water, also much shortened impeller life.
What size pipe is your inlet exactly (above it says 1.5-2") also what size is your output line. Measure exactly, and write down the number of 90s and 45s and the length of the piping.
There are flow charts for pvc that show frictional losses, you input those numbers and it will tell you how much head your pump is having to overcome. Then go to mdm's site and it will tell you how much flow it will have at that head loss, and how many watts its supposed to be using. That will tell you what size plumbing you need to do it right, or if you already have it right to begin with.
On the touching things with your hand note. Most of the time that is true. Now as I understand it, pumps are given a range of tempreture over ambient to operate in. Like some of them are ambeint plus 80f. that would be in your house 70+80=150f which can feel very hot. Some other ones run alot higher over ambient.
