Truck help 1991 Ford Ranger rpm?

So i have a couple problems i need to address. I noticed when driving my truck my rpms seem to be a little off. Its a manual so for example, when im in 3rd gear going 35 mph usually my rpms are about 2,100. Lately after it warms up the rpms are dropping 300-400 rpms. So when im in 3rd gear instead of 2,100 its like 1,700 or 1,800. If that makes sense. I just had clutch and slave cylinder replaced. Ive also noticed kind of a burning smell thought it might be low on clutch fluid checked that and it seemed fine… Any help?

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