the valve is leaking perchance? Put some soapy water on it and see if it bubbles. Maybe valve stem just needs tightening.

You may have a thorn or some other small, sharp object stuck in your tire. Such an object could cause both slow leaks.

Inflate just the tube and submerse it in water. If it bubbles at the valve, follow David's advice.

If it bubbles on the rubber part, you've found the hole. Next, slowly run your fingers inside the tire and probe for a sharp object.

-Deerslayer

Slime is stuff you put in tire, supposed to keep tires from going flat; doesn't work that well. Fix-a-flat works better, I have used both. My son uses a special thing to fill tire with water and finishes off with air, but I don't know what it is.

Also, if you put a tube in tire, stem shouldn't be leaking unless you cut it putting it in, that sometimes happens.

Just some tips I have learned over the years.

Olelady/Barbara

Did you feel inside the tire to see if something was sticking thru it causing the original leak and is still there puncturing the tube?

Walt Conner

I run slime in my LT but I dont think its recommended with tube tyres. tubeless only. Its great though. I have hawthorn hedges all around my property and before I filled the tyres with slime, I was getting punctures regularly. Havent had a puncture since...

Innertubes are now made with slime inside. Check the hardware store.

I had good luck with Slime on my old Snapper RER.

I put in tubes and the put slime in the tubes. Very seldom do I even add air. Until recently when all four were flat at one time. I assume some thorny stuff by the community trash can from somebody's elses yard got me.

Think I read you need to refresh the slime every couple of years. Mines probably got about 7 yrs on it.

Oh, yeah, i forgot about the "pre-slimed" tubes but I thought they were only for mountain bikes..? Havent seen them in LT tyres... cool, must keep an eye out for them.
The most satisfying thing about the slime (for me anyway) is when I have a thorn in my tyre and I pull it out with a pliars, a little dot of green shows and voilla, sorted... no flat...
I have the stuff in about 18 months now and have not had a flat since, prior to that, I had to pump tyres every time I wanted to mow the lawn... Worth its weight in gold that stuff.

Buy a new decent quality tyre. The normal ones are wafer thin.
You might even take the opportunity to put some wider wheels on. I used some off and old LT, the trailer is much less tippy now.

Another tip is if you have to replace the inner tube, cut the old one in half (cut the inside portion out) and then line the new tube with it. It then gives you more thickness and protection against thorns.

Metal,

Now that's a good idea.

Tubed every tire on all my implements long ago. No inflation troubles since. Heard of slime, but never needed it.

Metal,
I have to second lkbum's comment. That IS a really good idea. Got me to thinking, you can buy kevlar for $14 a yard (x54") on eBay. Maybe if you had an excessively thorny property it would be a good practice to line your tubed tires with that stuff. I wonder how puncture-resistant Kevlar is when it's not bonded in resin.

I used a slime-filled mountain bike tube once... just onece. As I inflated it it twisted, pinched, and ruptured. Never again. After working in a tire shop for several years, I always prefer to find the leak and use a good old patch (or plug).

How does this slime get inserted into the tire. Does it just get sprayed into the air valve under some kind of pressure?

You just remove the valve stem in then squeeze in the recommended amount and then replace the valve stem and air it up. You need to drive it a bit then to coat the inside of the tube.

Speaking of filling tires with foreign substances, on the farm we had all our vehicles(except diesels) switched over to propane. If we had a flat tire in the field we would just fill it with propane (we had a hose with adapters). It was such a common occurrence that the local Co-op had signs requesting that you inform them if tires you requested repair on had propane in them.