okay i don't know what to do here i have one mechanic that says my torque converter is bad and the other one says my spark plugs are bad....

Its vibrating not skipping and pressing the accelorator from like 55-60 or 45-50 and now when it changes gears it will jump in to it or you wont feel it at all while the RPM gage goes S-L-O-W-LY- down whereas usually it declines quickly

Any one on here have any suggestions.....I have had to have a lot put into this car since i have gotten it....it does have 140,000 miles on it...a dealer gave me trade value as $4,000 dollars! Should i take the offer and get the car i want or try and fix it?

Thanks!!