1999 Lincoln Continental Vacuum hose leak?

Engine Performance problem
1999 Lincoln Continental V8 Automatic 105, 00 miles

Hi, I am having problems seems like between 1st and 2nd and even 2nd to 3rd struggling. When I start to go, it struggles to get into gear it seems like, I have to back off the accelerator and start again and it accelerates like it should. It's not slipping though. Trying to explain the best I can. It's almost like I have it in park and it doesn't go anywhere when I try to accelerate. It growls and when I back off, and accelerate again, it progresses and I feel it kick into gear and it does it, not as much getting into 3rd. When I get up to 55 mph and up it performs fine. It's stopping at lights and stop signs it hesitates. Not always, but more lately. I was wondering if it could be a leak in a vaccuum hose because it doesn't feel like it's the transmission. I know the car has a rebuilt transmission in it because I have the receipt that was in the glove comp when I bought the car. Would a diagnostic test be in order? The engine light has been on lately, but it came on after my fiance fixed the suspension. (That was a quick slipping the part back into place for the automatic adjusting suspension. The part holdin it on came off somehow) I have since had to do it.) Anyway, that's all he did and the light has been on ever since. Coincidence? I don't know. The car has done this hesitating, off and on for a year now. It seemed to do it when I tried putting a cheaper gas in it, so I've stuck to premium and it's been fine until recently again. Maybe with gas being so high, they are doing something different to the premium like cutting it with methanol or something and my car doesn't like it. Any suggestions or help is greatly appreciated. Thank you!