I would check for fuel flow, air, and pressure at the top of the filter. There is a schrader fitting, press that and see if you get good flow (let it run a bit, not just a squirt). Do you have an ATV tire pressure gauge? Use a low pressure tire gauge to check the same schrader fitting for pressure... should have 5 psi or more. These two tests will quickly tell you if you have a supply (lift pump) problem. Just because you installed a new one does not mean that it is working, or that it was installed correctly.
After that, can you IP check timing? When cold do you have a noisier diesel rattle that quiets down once the cold advance comes off? This would indicate that you are 'close enough' that it should drive ok.
Since it drove well until you changed the lift pump I suspect you have a supply problem. Why did you change the lift pump (I don't need to know, you must have had a reason though)?
Glow plugs have nothing to do with it once the engine is running. You start well so you can eliminate that.
P.S. If you ever need to change your lift pump I would always recommend installing an electric. Well worth the effort!