My 2 cents...

Never use starter fluid (ether) on a gasoline engine. It was designed for diesel engines. Just pour a little gas in the carb.

1. Make sure you have a strong battery 900+ cranking amps. Take your battery in to get it checked out at battery supplier.

2. Make sure your posts are clean and wires & connectors are making good contact.

3. Do you have headers? Make sure they do not touch the starter. You will heat up the starter 100x faster if it's touching the header. Does the starter labor more when engine is hot?

4. Follow your fuel line to the carb. Make sure it does not make contact on anything hot. Your fuel could be getting too hot. If you have a clear inline fuel filter you can see it bubbling.

5. What temp is the engine at when it is turned off?

6. Do you have a flex, clutch or fixed fan? Do you have a fan shroud?

7. Do you have A/C filler panels and bottom baffle under the front?

I have always used a stock starter on my cars. I agree that the new ones would work much better though.

If your engine is running too hot you need to solve that first.