Only cold water in my tub hot only trickles

DRAIN AND FLUSH WATER HEATER

Is the hot water pressure good at other fixtures in the house? I'm guessing your newer valves have a scolding adjustment that is set very low. Check the instructions that came with the valve assembly.

Are your walls still open? I assume they are as you'd be unlikely to close them up without having had tested your water flow. Here is what I would do.
1.) use the orange plastic C shaped release tool to depress the white plastic ring on the shark bite fitting that you have on the delta side of the Delta-ShowerHead connection.
2.) Carefully and slowly turn water on and see if water is exiting the fixture where you expect it to.

IF yes, water is coming out of the delta fixture then you know the flow problem is somewhere between the delta fixture and your shower head.
IF no, water is not coming out the delta fixture then you need to re-access how you connected the supply lines to the delta fixture.

You have purchased a scald guard faucet, that you will have to set for your own house. If you take off the handle and face plate and look down there should be a plastic part (usually a deep blue) with teeth. It restricts the hot water side of the unit. If you pull it out and rotate (about halfway) you should have water flow. If it is still not hot enough rotate it more, or less.

Make sure the hot water is turned back on. Pressure balancing valves won't work if both cold and hot water is not on. Pull shower head off and test to see how it flows out of the shower arm. If good, clear out shower head. Whenever water is turned off for a time, and then turned back on, restricting shower heads and aerators usually get clogged. In the future, always open up a tub spout before turning water back on. This releases the air and other debris most effectively before testing other fixtures in the house.

Replace valve canister- no construction- just remove after taking time to shut off water- a few screws and the job takes 15 minutes. I take for granted you have good water hot/cold to the fixture. This fix will cure most temperature balance problems.
The single lever system is a EZ care system. Note the canister can malfunction faster when exposed to untreated hard water.

The Delta shower has a rotational limit stop designed so that when another fixture is activated, such as a toilet or dishwaser, the water does not go to extreme hot or cold. The reason for this is that the Delta shower unit is not pressure balanced or does not contain an anti scald device. The pdf document below will show how to adjust the water tempature if you feel it is too cold. Please use caution as it is probably set the way it is to prevent scalding.

http://www.deltafaucet.com/media/Product_Tech_Docs/Maint_Installation/50001to80000/51975RevH_4.15_15e05.pdf

change the cartridge it is bad or defective.

take handle off and adjust the nylon set ring it is to prevent kids from getting burned and is probably set wrong youll see teeth and a pointer just pull it out a little and turn it in the oppisite direction then push back in

sounds like you may have a little debri on hot side stem or kinked hose between valve and spout turn off water to house remove handle pull bonnet and remove stem turn water back on with stem removed see how water flow is be careful turning water on you could make a mess i am assuming the low pressure is in shower only